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Overlapped Subarray Architecture of an Wideband Phased Array Antenna with Interference Suppression Capability

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Journal of Electromagnetic Analysis and Applications 2013年第5期5卷 201-204页

作者： Quazi Md. Alfred tapas chakravarty Salil Kumar Sanyal Department of Electronics and Communication Engineering University Institute of Technology University of Burdwan Burdwan India Department of Electronics and Telecommunication Engineering Jadavpur University Kolkata India Tata Consultancy Services Kolkata India

This paper presents a novel architecture of combining the linear array of antenna elements, where each antenna element has digitally selectable true time-delays as weights. Use of time-delays for beam-formation inherently makes the phased array network a wideband system. In particular, this technique envisage a new method of sharing antenna elements, by fixed overlapped sub-array architecture, which is able to maintain permissible element spacing to avoid grating lobe in antenna pattern. Moreover, this scheme additionally offers an easier null steering capability to the subarray architecture. This method essentially eliminates the need for intensive computation of complex weight vectors attached to each antenna element.

关键词： Phased Array Subarray Time-Delay Overlapped Array

Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements

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Research in Astronomy and Astrophysics 2013年第11期13卷 1363-1380页

作者： tapas Baug Thyagarajan Chandrasekhar Physical Research Laboratory

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.

关键词： methods: analytical -- techniques: high angular resolution -- methods:lunar occultation -- infrared: stars -- stars: late type

Effect of Rare Earth and Transition Metal Elements on the Glass Forming Ability of Mechanical Alloyed Al–TM–RE Based Amorphous Alloys

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Journal of Materials Science & Technology 2015年第11期31卷 1118-1124页

作者： Ram S.Maurya tapas Laha Department of Metallurgical & Materials Engineering Indian Institute of Technology Kharagpur

The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.

关键词： Al-TM-RE amorphous alloy Mechanical alloying Glass forming ability Microstructural transformation Intermetallics Glass transition temperature

An efficient and comparative adsorption of Congo red and Trypan blue dyes on MgO nanoparticles: Kinetics, thermodynamics and isotherm studies

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Journal of Magnesium and Alloys 2021年第2期9卷 478-488页

作者： Barsharani Priyadarshini Tanaswini Patra tapas Ranjan Sahoo Department of Chemistry School of Applied SciencesKIIT deemed to be UniversityBhubaneswar 24OdishaIndia

Cubic phase of Mg O nanoparticles were prepared by microwave-assisted combustion synthesis and investigated for the removal of toxic dyes like Congo Red(CR)and Trypan blue(TB).The crystallite size of the Mg O nanoparticle was calculated to be 18 nm from XRD *** sample was further characterized by FTIR,TGA and FESEM *** dyes were subjected to prototypical batch adsorption process,including investigation of different parameters like Mg O dosage,dye concentration,solution pH,agitation speed and *** was found that,0.2 g of Mg O NPs showed maximum removal efficiency for both the dyes(more than 98%),having 25 ppm of dye concentration at an acidic p H(3–4).The maximum loading capacity of Mg O NPs was obtained to be 136 mg/g and 132 mg/g for CR and TB,*** thermodynamic parameters like△G^(0),△H^(0)and△S^(0)were *** negative△H^(0)and the positive△S^(0)values for both the dyes correspond to an exothermic process and an increase in randomness of the adsorbent and *** isotherm analysis exhibited that the Freundlich model fits better to the experimental equilibrium data,suggesting heterogeneous surface of the ***,the kinetic data revealed a pseudo 2 nd order rate for adsorption process.

关键词： Adsorption Congo red Trypan blue MgO NPs Kinetics Isotherm

Effect of sintering temperature on phase evolution of Al86Ni6Y4.5Co2La1.5 bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

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Progress in Natural Science:Materials International 2019年第1期29卷 32-40页

作者： Ashutosh Sahu Ram Sajeevan Maurya tapas Laha Department of Metallurgical and Materials Engineering Indian Institute of Technology Department of Metallurgical and Materials Engineering National Institute of Technology

Al86Ni6Y4.5Co2La1.5amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.

关键词： Al based glassy alloy Mechanical alloying Spark plasma sintering Intermetallic phase Viscosity

An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

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Journal of Energy Chemistry 2021年第8期30卷 160-190,I0005页

作者： Subhasis Shit Saikat Bolar Naresh Chandra Murmu tapas Kuila Surface Engineering&Tribology Division Council of Scientific and Industrial Research-Central Mechanical Engineering Research InstituteMahatma Gandhi AvenueDurgapur 713209India Academy of Scientific and Innovative Research(AcSIR) CSIR-Human Resource Development Centre(CSIR-HRDC)CampusPostal Staff College AreaSector 19Kamla Nehru NagarGhaziabad 201002India

The electrolysis of water for hydrogen generation has shown immense promise as an energy conversion technology for the green energy *** concurrently occurring electrochemical reactions in water electrolysis(hydrogen and oxygen evolution reactions)are sluggish in nature and therefore the employment of electrocatalysts is highly ***-metal-based electrocatalysts(Pt,Ru O_(2),Ir O_(2),etc.)have shown superior activity towards these ***,their lower natural abundance and inferior stability make the cost to performance ratio of water electrolysis too ***,huge amount of research efforts are being carried out to develop electrocatalysts consisting of earth abundant elements(transition metals,carbon etc.)as the replacement of these noble-metal-based *** metal compounds,carbonaceous and hybrid materials have shown promise as efficient electrocatalysts but there is still huge gap between the activities of these materials and the noble-metal-based *** strategies like morphology modulation,elemental doping,defect engineering *** being deployed to enhance the activity of these noble-metal-free *** review summarizes these strategies and thoroughly discusses the reason behind the changes in activity of the electrocatalysts owing to these ***,the remaining research gaps and future prospects in this field are also discussed in detail.

关键词： Water splitting Electrocatalyst Morphology Doping Defect engineering Phase engineering

Effect of Sintering Temperature and Heating Rate on Crystallite Size,Densification Behaviour and Mechanical Properties of Al-MWCNT Nanocomposite Consolidated via Spark Plasma Sintering

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Acta Metallurgica Sinica(English Letters) 2018年第10期31卷 1019-1030页

作者： Lavish Kumar Singh Alok Bhadauria Subhodeep Jana tapas Laha Department of Metallurgical and Materials Engineering Indian Institute of Technology Kharagpur Kharagpur India Centre for Healthcare Science and Technology Indian Institute of Engineering Science and Technology Shibpur India

Powder mixture of ball-milled aluminium and functionalized multi-walled carbon nanotubes was compacted via spark plasma sintering （SPS） to study effects of sintering temperature and heating rate. An increase in sintering temperature led to an increase in crystallite size and density, whereas an increase in heating rate exerted the opposite effect. The crystallite size and relative density increased by 85.0% and 14.3%, respectively, upon increasing the sintering temperature from 400 to 600℃, whereas increasing the heating rate from 25 to 100 ℃/min led to respective reduction by 30.0% of crystallite size and 1.8% of relative density. The total punch displacement during SPS for the nanocomposite sintered at 600 ℃ （1.96 mm） was much higher than that of the sample sintered at 400 ℃ （1.02 mm） confirming positive impact of high sintering temperature on densification behaviour. The maximum improvement in mechanical properties was exhibited by the nanocomposite sintered at 600 ℃ at a heating rate of 50℃/min displaying microhardness of 81 4- 3.6 VHN and elastic modulus of 89 4- 5.3 GPa. The nanocomposites consolidated at 400 ℃ and 100 ℃/min, in spite of having relatively smaller crystallite size, exhibited poor mechanical properties indicating the detrimental effect of porosity on the mechanical properties.

关键词： Al nanocomposite Multi-walled carbon nanotubes Ball milling Spark plasma sintering Densification behaviour Mechanical properties

Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

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Research in Astronomy and Astrophysics 2024年第6期24卷 81-93页

作者： Arijit Manna Sabyasachi Pal tapas Baug Sougata Mondal Department of Physics Midnapore City CollegePaschim MedinipurWest Bengal721129India S.N.Bose National Centre for Basic Sciences Block-JDSector-IIISalt Lake CityKolkata700106 India

The observation of oxygen(O)-and nitrogen(N)-bearing molecules gives an idea about the complex prebiotic chemistry in the interstellar *** millimeter and submillimeter wavelength observations have shown the presence of complex O-and N-bearing molecules in the star formation ***,the investigation of those molecules is crucial to understanding the chemical complexity in the star-forming *** this article,we present the identification of the rotational emission lines of N-bearing molecules ethyl cyanide(C_(2)H_(5)CN)and cyanoacetylene(HC_(3)N),and O-bearing molecule methyl formate(CH_(3)OCHO)toward high-mass protostar IRAS18089–1732 using the Atacama Compact *** also detected the emission lines of both the N-and O-bearing molecule formamide(NH_(2)CHO)in the envelope of IRAS 18089–*** have detected the v=0 and 1 state rotational emission lines of CH_(3)*** also detected the two vibrationally excited states of HC_(3)N(v7=1 and v7=2).The estimated fractional abundances of C_(2)H_(5)CN,HC_(3)N(v7=1),HC_(3)N(v7=2),and NH_(2)CHO toward IRAS 18089–1732 are(1.40±0.5)×10^(-10),(7.5±0.7)×10^(-11),(3.1±0.4)×10^(-11),and(6.25±0.82)×10^(-11)***,the estimated fractional abundances of CH_(3)OCHO(v=0)and CH_(3)OCHO(v=1)are(1.90±0.9)×10^(-9)and(8.90±0.8)×10^(-10),*** also created the integrated emission maps of the detected molecules,and the observed molecules may have originated from the extended envelope of the *** show that C_(2)H_(5)CNand HC_(3)N are most probably formed via the subsequential hydrogenation of the CH_(2)CHCNand the reaction between C_(2)H_(2)and CN on the grain surface of IRAS 18089–*** found that NH_(2)CHO is probably produced due to the reaction between NH_(2)and H_(2)CO in the gas ***,CH_(3)OCHO is possibly created via the reaction between radical CH_(3)O and radical HCO on the grain surface of IRAS 18089–1732.

关键词： ISM:individual objects(IRA 18089-1732)(except) ISM:abundances ISM:kinematics and dynamics stars:formation astrochemistry

Analyzing the Effects of Milling and Sintering Parameters on Crystalline Phase Evolution and Mechanical Properties of Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) Amorphous Ribbons

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Acta Metallurgica Sinica(English Letters) 2022年第6期35卷 1043-1054页

作者： Ashutosh Sahu Ram Sajeevan Maurya Lavish Kumar Singh tapas Laha Department of Mechanical Engineering School of Engineering and TechnologySharda UniversityGreater Noida 201310India Department of Metallurgy Engineering and Materials Science Indian Institute of Technology IndoreIndore 453552India Department of Metallurgical and Materials Engineering Indian Institute of Technology KharagpurKharagpur 721302India

In the present study,Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) bulk amorphous nanocomposites were synthesized by spark plasma sintering of milled melt spun ribbon *** as-cast ribbons were of near amorphous nature with minute amount of FCC Al embedded in the amorphous *** of the ribbons resulted in partial devitrifi cation due to mechanical *** milled ribbon particles were sintered in the temperature and pressure range of 300-500℃ and 500-700 MPa,*** was observed that nominal amount of amorphous phase was retained at 500℃ and 500 *** increase in sintering pressure and decrease in sintering temperature,the amount of crystalline phase evolution decreased,and maximum amount of amorphous phase was retained at 300℃ and 700 *** microstructure consisting of amorphous phase embedded with hard intermetallic phases led to increase in the nanohardness of Al_(86)Ni_(8)Y_(6) and Al_(86)Ni_(6)Y_(4.5)Co_(2)La_(1.5) as-cast ribbons from 3.26±0.59 GPa and 3.81±0.58 GPa to 6.06±0.70 GPa and 6.14±0.82 GPa,respectively,for the corresponding consolidated amorphous *** of the three and five component system bulk samples was 4.19±0.13GPa and 3.6±0.13 GPa,respectively.

关键词： Amorphous alloy Milled ribbon Spark plasma Sintering Nanohardness Internetallic compound