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Journal of materials Science & Technology 2012年第4期28卷 329-335页

作者： m. mozibur rahman m.k.r. khan m. rafiqul Islam m.a. Halim m. Shahjahan m.a. hak.m.dilip k.m.r saha Jasim Uddin khan Department of Physics University of Rajshahi Rajshahi 6205 Bangladesh materials Science Division Atomic Energy Centre Dhaka Bangladesh Industrial Physical Division BCSIR Dhaka Bangladesh

The nano-structural Al-doped ZnO thin films of different morphologies deposited on glass substrate were successfully fabricated at substrate temperature of 350 ℃ by an inexpensive spray pyrolysis method. The structural, electrical, optical and photoluminescence properties were investigated. X-ray diffraction study revealed the crystalline wurtzite （hexagonal） structure of the films with nano-grains. Scanning electron microscopy （SEm） micrographs indicated the formation of a large variety of nano-structures during film growth. The spectral absorption of the films occurred at the absorption edge of -410 nm. In the present study, the optical band gap energy 3.28 eV of ZnO decreased gradually to 3.05 eV for 4 mol% of AI doping. The deep level activation energy decreased and carrier concentrations increased substantially with increasing doping. Exciting with the energy 3.543 eV （A=350 nm）, a narrow and a broad characteristic photoluminescence peaks that correspond to the near band edge （NBE） and deep level emissions （DLE）, respectively emerged.

关键词： Thin film Nano-structure ZnO Surface morphology Photolumlnescence

Lesser Himalayan sequences in Eastern Himalaya and their deformation:Implications for Paleoproterozoic tectonic activity along the northern margin of India

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Geoscience Frontiers 2013年第3期4卷 289-304页

作者： dilip saha Geological Studies Unit Indian Statistical Institute203 B.T.RoadKolkata 700108India

Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence （LHS） of Eastern Himalaya, namely the Daling Group in Sikkim.a.d the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite- slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic-mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here：（1） the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; （2） the older deformation and metamorphism relate to a Pacific type accretionary orogen wh

关键词： Garnet composition kinematics Lesser Himalayan sequence microstructure Paleoproterozoic Supercontinent

Effect of Co doping on structural, optical, electrical and thermal properties of nanostructured ZnO thin films

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Journal of Semiconductors 2015年第3期36卷 35-40页

作者： Sonet k.m.r saha m.a.izar rahman m.r.H.Sarkar m.Shahjahan m.k.r.khan Department of Physics Bangladesh University of Engineering and Technology Department of Physics University of Rajshahi

Nanocrystalline Zn1-x CoxO（where x varies from 0 to 0.04 in steps of 0.01） thin films were deposited onto glass substrate by the spray pyrolysis technique at a substrate temperature of 350 ℃. The X-ray diffraction patterns confirm the formation of hexagonal wurtzite structure. The crystal grain size of these films was found to be in the range of 11–36 nm. The scanning electron micrographs show a highly crystalline nanostructure with different morphologies including rope-like morphology for undoped ZnO and nanowalls and semispherical morphology for Co-doped Zn O. The transmittance increases with increasing Co^2＋ doping. The optical absorption edge is observed in the transmittance spectra from 530 to 692 nm, which is due to the Co2C absorption bands corresponding to intraionic d–d^＊ shifts. The direct and indirect optical band gap energies decrease from 3.05 to 2.75 eV and 3.18 to 3.00 eV, respectively for 4 mol% Co doping. The electrical conductivity increases with increasing both the Co doping and temperature, indicating the semiconducting nature of these films. The temperature dependence thermal electromotive force m.a.urement indicates that both undoped and Co-doped ZnO thin films show p-type semiconducting behavior near room temperature. This behavior dies out beyond 313 k and they become n-type semiconductors.

关键词： ZnO:Co thin films structural properties optical properties electrical properties thermal properties

Tuff beds in kurnool subbasin,southern India and implications for felsic volcanism in Proterozoic intracratonic basins

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Geoscience Frontiers 2012年第4期3卷 429-444页

作者： dilip saha Vikash Tripathy Geological Studies Unit lndian Statistical InstituteKolkata 700108India A-1/79 Sector-18RohiniNew Delhi 110089India

A first report on tuff beds from the Owk Shale in the Proterozoic kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave base, have rheomorphie features indicative of viscoplastic flow, and geochem- ical signatures of rhyolitic to rhyodacitic unwelded to welded tufts, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag- matic reactions. The widespread and repeated occurrences of felsic tufts in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.

关键词： Felsic tuff Intracratonic basin kumool subbasin Owk Shale Proterozoic

Influence of Annealing Conditions on Nanocrystalline and Ultra-Soft magnetic Properties of Fe_(75.5)Cu_1Nb_1_Si_(13.5)B_9 Alloy

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Journal of materials Science & Technology 2012年第1期28卷 21-26页

作者： S.P. mondal kazi Hanium maria S.S. Sikder Shamima Choudhury D.k. saha m.a. hakim Department of Physics Khulna University of Engineering & TechnologyKhulna-9203Bangladesh Department of Physics University of DhakaDhaka-1000Bangladesh materials Science Divisions Atomic Energy CentreDhaka-1000DhakaBangladesh

The magnetic and structural properties of FINEmET alloy with a composition of ***1Nb1Si13.5B9 were investigated after primary and secondary crystallization of amorphous ribbon sample. The crystallization behavior and the nanocrystal formation of the samples were performed by differential thermal analysis （DTA） which in turn was supported by X-ray diffraction （XrD） study. Temperature dependence of initial perm.a.ility of amorphous and devitrified toroid shaped samples has been m.a.ured. Enhancement of Curie temperature of the amorphous alloy has been observed due to the irreversible structural relaxation. With the appearance of nanocrystalline phase the Curie temperature of the residual amorphous phase gradually decrease with the increase of annealing temperature. Their temperature dependence reflects the characteristic annealing temperature evolution of the basic magnetic parameters in these nanocrystalline systems. Saturation magnetization, ms, increases with annealing temperature Ta for the samples and finally decreases during annealing at a temperature much higher than peak crystallization temperature.

关键词： Nanostuctured alloy Curie temperature Saturation magnetization

Combined effect of reynolds and Grashof numbers on mixed convection in a lid-driven T-shaped cavity filled with water-Al_2O_3 nanofluid

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Journal of Hydrodynamics 2015年第5期27卷 782-794页

作者： mOJUmDEr Satyajit saha Sourav saha Sumon mAmUN m.a.H. Department of mechanical Engineering Bangladesh University of Engineering and Technology

Lid-driven mixed convection has been given immense importance due to its wide range of applications. A T-shaped cavity is introduced and pertinent parameters controlling mixed convection phenomenon are analyzed in this paper. Water-Al2O3 nanofluid is considered inside the cavity to augment heat transfer rate. Galerkin weighted residual method of finite element analysis is applied for the numerical simulations. Numerical solution is obtained for different solid volume fractions of nanofluid（？= 0- 0.15）, Grashof numbers（Gr= 0.1 ？5 000） and reynolds numbers（re= 0.31 ？1 000） in laminar flow regime. Special attention is given on the analysis of flow at the pure mixed convection regime. It is found that Grashof, reynolds and richardson numbers along with solid volume fraction of nanofluid have significant effect on heat transfer characteristics inside the cavity. results are presented using streamline and isotherm contours along with related variation of average Nusselt numbers of the heated wall and average fluid temperature inside the cavity.

关键词： mixed convection nanofluid lid-driven T-shaped richardson number finite element

Effect of Hall current on mHD natural convection flow from vertical perm.a.le flat plate with uniform surface heat flux

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Applied mathematics and mechanics(English Edition) 2011年第9期32卷 1127-1146页

作者： L.k.saha S.SIDDIQA m.a.HOSSAIN Department of mathematics University of DhakaDhaka 1000Bangladesh Department of mathematics COMSATS Institute of Information TechnologyPark RoadChak ShahzadIslamabad 44000Pakistan

The effect of the Hall current on the magnetohydrodynamic （mHD） natural convection flow from.a.vertical perm.a.le flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic *** is assumed that the induced magnetic field is negligible com.a.ed with the imposed magnetic *** boundary layer equations are reduced to a suitable form by employing the free variable formulation （FVF） and the stream function formulation （SFF）.The parabolic equations obtained from FVF are numerically integrated with the help of a straightforward finite difference ***,the nonsimilar system of equations obtained from SFF is solved by using a local nonsimilarity method,for the whole range of the local transpiration parameter ζ.Consideration is also given to the regions where the local transpiration parameter ζ is small or large ***,in these particular regions,solutions are acquired with the aid of a regular perturbation *** effects of the magnetic field m.a.d the Hall parameter m on the local skin friction coefficient and the local Nusselt number coefficient are graphically shown for smaller values of the Prandtl number P r （= 0.005,0.01,0.05）.Furthermore,the velocity and temperature profiles are also drawn from various values of the local transpiration parameter ζ.

关键词： magnetohydrodynamic (mHD) natural convection Hall current perm.a.le plate heat flux

Field-dependent spin waves in high-aspect-ratio singlecrystal ferromagnetic nanowires

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Nano research 2016年第5期9卷 1426-1433页

作者： Semanti Pal Susmita saha m. Venkata kamalakar Anjan Barman Department of Condensed matter Physics and material Sciences S. N. Bose National Centre for Basic Sciences Block JD Sector Ⅲ Salt Lake Kolkata 700 098 India Department of Physics and Astronomy Uppsala University Box 516 75120 Uppsala Sweden

We investigate the spin wave （SW） modes in high-aspect-ratio single-crystal ferromagnetic nanowires （FmNWs） using an all-optical time-resolved magnetooptical kerr effect （Tr-mOkE） microscope. The precessional magnetization dynamics in such FmNWs unveil the presence of uniform.a.d quantized SW modes that can be tuned by varying the bias magnetic field （H）. The frequencies of the modes are observed to decrease systematically with a decreasing magnetic field, and the number of modes in the spectrum is reduced from four to three for H 〈 0.7 kOe. To understand these results, we perform micromagnetic simulations that reveal the presence of edge, standing wave, and uniform SW modes in the nanowires （NWs）. Our simulations clearly show how the standing wave and uniform SW modes coalesce to form.a.single mode with uniform precession over the entire NW for H 〈 0.7 kOe, reproducing the experimentally observed reduction in modes. Our study elucidates the possibility of manipulating the SW modes in magnetic nanostructures, which is useful for applications in magnonic and spintronic devices.

关键词： Field-dependent high-aspect-ratio nanowires

mQTT and blockchain sharding:An approach to user-controlled data access with improved security and efficiency

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Blockchain(research and Applications) 2023年第4期4卷 86-98页

作者： P.S.Akshatha S.m.dilip k.m.r Department of Computer Science and Engineering University of Visvesvaraya College of EngineeringBangalore UniversityBengaluruKarnataka 560056India

The rapid growth of the Internet of Things(IoT)has raised security concerns,including mQTT protocol-based applications that lack built-in security features and rely on resource-intensive Transport Layer Security(TLS)*** paper presents an approach that utilizes blockchain technology to enhance the security of mQTT communication while maintaining *** approach involves using blockchain sharding,which enables higher scalability,improved performance,and reduced computational overhead com.a.ed to traditional blockchain approaches,making it well-suited for resource-constrained IoT *** approach leverages Ethereum blockchain’s smart contract mechanism to ensure trust,accountability,and user ***,we introduce a shard-based consensus mechanism that enables improved security while minimizing computational *** also provide a user-controlled and secured algorithm using Proof-of-Access implementation to decentralize user access control to data stored in the blockchain *** proposed approach is analyzed for usability,including metrics such as bandwidth consumption,CPU usage,memory usage,delay,access time,storage time,and jitter,which are essential for IoT application *** analysis demonstrated that the approach reduces resource consumption,and the proposed system outperforms TLS and existing blockchain approaches in these metrics,regardless of the choice of the mQTT ***,thoroughly addressing future research directions,including issues and challenges,ensures careful consideration of potential advancements in this domain.

关键词： Blockchain Internet of Things mQTT Publish/Subscribe mQTT brokers HivemQ mosquitto EmQx Eclipse Sharding

Conduction-radiation effect on natural convection flow in fluid-saturated non-Darcy porous medium enclosed by non-isothermal walls

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Applied mathematics and mechanics(English Edition) 2013年第6期34卷 687-702页

作者： m. A. HOSSAIN m. SALEEm S. C. saha A. NAkAYAmA Department of mathematics COMSATS Institute of Information Technology School of Chemistry Physics & Mechanical Engineering Queensland University of Technology Department of mechanical Engineering Shizuoka University

The combined effect of conduction-convection-radiation on natural convec- tion flow of an optically thick Newtonian fluid with gray radiant properties, confined in a porous media square cavity with Darcy-Brinkman-Forchheimer drag is studied numeri- cally. For a gray fluid, rosseland diffusion approximation is considered. It is assumed that （i） the temperature of the left vertical wall varies linearly with height, （ii） the right vertical and top walls are at a lower temperature, and （iii） the bottom wall is uniformly-heated. The governing equations are solved using the alternate direct implicit method together with the successive over relaxation technique. The investigation of the effect of governing parameters, namely, the Forschheimer resistance （F）, the temperature difference （A）, and the Plank number （rd）, on the flow pattern and heat transfer characteristics is carried out. It can be seen that the reduction of flow and heat transfer occur as the Forschheimer resistance is increased. On the other hand, both the flow strength and heat transfer in- crease as the temperature ratio A is increased.

关键词： conduction-convection-radiation,Darcy-Brinkman-Forchheimer drag porousmedium enclosure