Numerical Study on Tide and Tidal Current along Bali Strait, Indonesia using Finite Volume Coastal Ocean Model (FVCOM)

Made Narayana Adibhusana(Made Narayana Adibhusana ),유용욱(Yonguk Ryu) 한국연안방재학회 2023 한국연안방재학회지 Vol.10 No.1

A numerical study was carried out in Bali Strait, Indonesia. Finite Volume Coastal Ocean Model (FVCOM) was used to simulate the seawater circulation in Bali Strait. The water circulations were forced by the four major tidal components (S2, M2, K1 , and O1). Comparisons of the seawater surface elevation obtained from both modeling and observations show a good result. The tide in Bali Strait is a mixed tide type with two different tidal ranges in one day. The seawater circulation moves from the Indian Ocean to the Bali Sea through narrow strait during the flood tide and then rush back during the ebb tide. In the spring tide, an eddy is also observed on the top of the narrow strait. The simulations show that the flows by tides along the sudden change of the cross-sectional width can be modeled by the finite volume method based model.

Tensile properties of a newly developed high-temperature titanium alloy at room temperature and 650 °C

Narayana, P.L.,Kim, Seong-Woong,Hong, Jae-Keun,Reddy, N.S.,Yeom, Jong-Taek Elsevier 2018 Materials science & engineering. properties, micro Vol.718 No.-

<P><B>Abstract</B></P> <P>Commonly used high-temperature near-alpha titanium alloys contain Al, Zr and Si as their alloying elements. Significant losses of mechanical properties and cleavage mode failures are evident due to the presence of Ti3Al and S2 types of zirconium silicides ((TiZr)6Si3) in these alloys. We developed a new alloy (Ti-6.5Al-3.0Sn-4.0Hf-0.2Nb-0.4Mo-0.4Si-0.1B) by replacing Zr with Hf to avoid the formation of zirconium silicides. Aging at 700 °C for five hours successfully eliminated the Ti3Al phase and substantially improved the room-temperature ductility. Tensile tests were carried out at room temperature and at 650 °C. The mechanical properties of the present alloy were significantly improved compared to those of existing high-temperature titanium alloys under testing at ambient and elevated temperatures.</P>

Class Based Dynamic Feature Centric Data De-duplication Scheme for Efficient Mitigation of Side Channel Attack in Cloud

Narayana K. E.,Jayashree K. 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.3

Towards efcient data storage and maintenance in cloud, diferent privacy preservation and data deduplication schemes are presented in literature. However, the methods sufer to mitigate side channel attacks in cloud which challenges the data security. To handle this, an efcient Class based Dynamic Feature Centric Data De-duplication (CDFC-DD) is presented in this article. The method classifes the data and features under several classes according to their sensitivity. In this way, the method enforces efective access restriction scheme in class level using Class based Access Restriction Scheme (CARS) with the use of client profle. The method would compute the class level trust measure (CLTM) based on which access restriction is performed. Similarly, the method maintains a feature matrix, which contains the class of feature and indexes belongs to the feature, scheme and key. By computing Legitimate Access Measure (LAM) value, the method performs data deduplication. Also, the data has been involved in two way data encryption which encrypts the data with the feature key by the user where it has been re-encrypted using class key to improve the security performance. The proposed CDFC-DD scheme improves data security and improves the QoS of the environment. The Proposed method fnds the data identifying a specifc owner, and validation ensures that authenticated data at least corresponds exactly to a set of users in cloud storage. Simulation results show the Access restriction (AR), Encryption/Decryption Performance and Time Complexity (T) for increasing performance based on the CDFC-DD better than the existing method.

Raman gain in a Boron based Group-III nitride quantum well

Narayana Moorthy, N.,John Peter, A.,Lee, C.W. Academic Press 2014 Superlattices and microstructures Vol.70 No.-

Electron Raman scattering of a hydrogenic impurity is studied using exact diagonalization method in a B<SUB>x</SUB>Ga<SUB>1-x</SUB>N/BN coupled quantum well. Intersubband scattering rates, in a Boron based wide band gap GaN, are considered. B<SUB>x</SUB>Ga<SUB>1-x</SUB>N semiconductor is taken as inner quantum well and BN material is taken as barrier material. The effect of quantum confinement on the differential cross section of Raman scattering, with and without the impurity, is obtained. The built-in internal electric field is included throughout the calculations. The third order susceptibility with the incident photon energy is calculated with and without doping impurity. The donor hydrogenic binding energy and its low lying excited states are computed taking into account the geometrical confinement. The binding energy is obtained for various impurity position and the Boron alloy content in B<SUB>x</SUB>Ga<SUB>1-x</SUB>N quantum well. It is brought out that the geometrical confinement and built-in internal electric fields have great influence on the optical properties of the semiconductor.

Microstructural response of β-stabilized Ti–6Al–4V manufactured by direct energy deposition

Narayana, P.L.,Lee, Sangwon,Choi, Seong-Woo,Li, Cheng-Lin,Park, Chan Hee,Yeom, Jong-Taek,Reddy, N.S.,Hong, Jae-Keun Elsevier 2019 Journal of Alloys and Compounds Vol.811 No.-

<P><B>Abstract</B></P> <P>The present study describes the influence of β stabilizers (namely Fe and Cr) on the microstructural evolution and mechanical behavior of Ti–6Al–4V alloy fabricated by direct energy deposition. As the β stabilizer content increases from 1 to 4 wt%, the coarse columnar-grained morphology typical of additively manufactured Ti–6Al–4V is significantly refined, with a columnar-to-equiaxed transition. Furthermore, reheating of the deposited layers by the deposition of overlaying layers during fabrication induces an element partitioning effect, resulting in the formation of fine-grained α and isothermal ω. Hence, the heat profile during direct energy deposition resembles conventional solution and aging treatments. In addition, increasing the amount of β stabilizer steadily increases the room temperature strength of the Ti–6Al–4V alloy. The alloy with 4 wt% Fe showed the maximum strength, of ∼1.5 GPa.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The columnar-to-equiaxed transition of microstructure was achieved in the direct energy deposited Ti–6Al–4V alloy with the addition of Fe and Cr. </LI> <LI> The maximum room temperature strength of the Ti–6Al–4V with 4 wt% Fe alloy reaches ∼1.5 GPa. </LI> <LI> The reheating phenomenon caused by deposition of overlying layers during direct energy deposition resembles conventional solution and aging treatments. </LI> <LI> With an increasing amount of β stabilizer, the phase constituents in the Ti–6Al–4V alloy changed from αʹ .→ αʹ+α+ω+β → α+ω+β </LI> </UL> </P>

Survey of Group Key Management Techniques in MANET

G.Narayana,M.Akkalakshmi,A.Damodaram 보안공학연구지원센터 2016 International Journal of Future Generation Communi Vol.9 No.11

Group key management (GKM) technique is employed for ensuring security and integrity in Mobile Ad hoc Networks (MANET). It is the fundamental component of secure group communication systems. It involves distribution, updation and revocation of group keys. GKM can be carried out through many approaches. Existing studies on GKM techniques in MANET did not provide detailed analysis. This survey presents various GKM techniques for MANETs. The existing GKM techniques are classified into three categories namely centralized, distributed and hierarchical. Each of these techniques are explained with their advantages and disadvantages.

Development of slag based Shirasu geopolymer

Dhruva Narayana Katpady,Koji Takewaka,Toshinobu Yamaguchi 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.1

Shirasu, a pyroclastic flow deposit, showed considerable performance as aluminosilicate source in geopolymer, based on past research. However, the polymerization reactivity was somewhat lower compared to the traditional fly ash based geopolymer even though the long-term strength was fairly good. The present study concentrates on the development of higher initial strength performance of Shirasu based geopolymer by utilizing ground granulated blast furnace slag as an admixture. Mortars with various mix proportions were adopted to study the effect of parametric changes on strength development along with the addition of slag in different percentages. A combination of sodium hydroxide and sodium silicate was used as alkaline activators considering parameters like molar ratios of alkali to geopolymer water and silica to alkali molar ratio. The mortars were cured at elevated temperatures under different curing conditions to analyze the effect on strength development. Compressive strength test, mercury intrusion porosimetry and X-ray powder diffraction were carried out to assess the strength performance and microstructure of slag-Shirasu based geopolymer. Based on the experimental study, it was observed that the initial and long-term strength development of Slag-Shirasu geopolymer were improved by the addition of slag.

A Review on the Atmospheric Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in Asia Since 2000 - Part I: Data from Developed Countries

Lakshmi Narayana Suvarapu,서영교,Beom-Seok Lee,Sung-Ok Baek 한국대기환경학회 2012 Asian Journal of Atmospheric Environment (AJAE) Vol.6 No.3

Among all hazardous air pollutants, polycyclic aromatic hydrocarbons (PAHs) are more significant owing to their carcinogenic, mutagenic and teratogenic properties. Many researchers worldwide have focused on determining the concentrations of PAHs in ambient air. However, the literature survey reveals that the seriousness of air pollution in Asia in terms of PAHs, compared to the rest of the world. Owing to the importance of PAHs in Asia, this paper reviews the concentrations of PAHs in Asia in recent years. For convenience, this paper describes the concentrations of PAHs in developed Asian countries reported during 2000-2011 as Part-I and in developing Asian countries as Part-II. The first section of this review provides a brief description of the properties, sources of PAHs and the health effects caused by their presence in the atmosphere. The ambient air PAH concentrations in both particle and vapor phases in developed Asian countries are then discussed. This study finds the ambient air concentrations of PAHs in developed Asian countries was higher than the Western countries but was lower than the developing Asian countries. The present review predicts the accurate toxicity due to the presence of PAHs in the atmosphere by calculating the Risk Weighted Concentration (RWC), regardless of the total amount of PAHs. The total data obtained during the literature survey is tabulated and presented as supplementary information to the readers. Among all hazardous air pollutants, polycyclic aromatic hydrocarbons (PAHs) are more significant owing to their carcinogenic, mutagenic and teratogenic properties. Many researchers worldwide have focused on determining the concentrations of PAHs in ambient air. However, the literature survey reveals that the seriousness of air pollution in Asia in terms of PAHs, compared to the rest of the world. Owing to the importance of PAHs in Asia, this paper reviews the concentrations of PAHs in Asia in recent years. For convenience, this paper describes the concentrations of PAHs in developed Asian countries reported during 2000-2011 as Part-I and in developing Asian countries as Part-II. The first section of this review provides a brief description of the properties, sources of PAHs and the health effects caused by their presence in the atmosphere. The ambient air PAH concentrations in both particle and vapor phases in developed Asian countries are then discussed. This study finds the ambient air concentrations of PAHs in developed Asian countries was higher than the Western countries but was lower than the developing Asian countries. The present review predicts the accurate toxicity due to the presence of PAHs in the atmosphere by calculating the Risk Weighted Concentration (RWC), regardless of the total amount of PAHs. The total data obtained during the literature survey is tabulated and presented as supplementary information to the readers.

An overview of device-to-device communication in cellular networks

Udit Narayana Kar,Debarshi Kumar Sanyal 한국통신학회 2018 ICT Express Vol.4 No.4

Device-to-device (D2D) communication is expected to play a significant role in upcoming cellular networks as it promises ultra-low latency for communication among users. This new mode may operate in licensed or unlicensed spectrum. It is a novel addition to the traditional cellular communication paradigm. Its benefits are, however, accompanied by many technical and business issues that must be resolved before integrating it into the cellular ecosystem. This paper discusses the main characteristics of D2D communication including its usage scenarios, architecture, technical features, and areas of active research.

Relation of change in geometrical parameters in the thermal performance of solar chimney

Biranchi Narayana Padhi,Mukundjee Pandey,Ipsita Mishra 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.10

The article deals with the effects of change in dimensions of solar chimney upon the thermodynamic characteristics of the air flowing inside it. The solar chimney at Manzanares (Spain) has been selected as the base model for this study. ANSYS-Discovery-Aim 2019 R1 has been used for the simulation of different geometric variations of solar chimney along with its validation with the work by Haaf et al. It is found that of all the geometric changes, the increase in roof height is undesirable. While for others like increase in chimney height, increase in chimney diameter and increase in collector radius gives desirable results in terms of increase in velocity of air. Also, for the case with an increase in chimney diameters; it is found to be suitable if the turbines are placed at the outlet of the collector and not within the chimney.