1,399 research outputs found
Experimental evaluation of long term evolution-based NC OFDM secondary-to-secondary interference
No full textScarcity of spectrum resources, inefficient spectrum usage and the inflexibility of the current spectrum assignment are few of the major roadblocks in the development of new wireless communication standards. Secondary spectrum sharing has become a viable solution to alleviate this problem. Secondary users are unlicensed devices that use opportunistic spectrum access to identify vacant frequency bins and thereby utilize the spectrum. For advanced wireless communication standards like the Long Term Evolution (LTE) which primarily calls for higher data rates, evaluation of design parameters for ensuring efficient coexistence of heterogeneous secondary users and guaranteeing acceptable minimum level of performance becomes essential. Additionally, the understanding of the interference between secondary users occupying adjacent frequency bands for their transmission is imperative. This thesis focuses on the coexistence of secondary users in the same band assuming that the primary spectrum is found available. By Implementing two Non Contiguous Orthogonal Frequency Division Multiplexing ( NC-OFDM) based secondary transmitters on a real time platform, the design parameters that need to be considered to ensure efficient coexistence have been identified and investigated. The performance degradations observed at a particular secondary link due to presence of another interfering secondary link occupying adjacent frequency bands for its transmission have also been studied. This thesis also focuses on implementation of algorithms to modify the existing NC-OFDM transmission at the secondary transmitter end to reduce its Interference effects on the other secondary links operating within the same band. The focus is on an LTE-based Secondary Non Contiguous Orthogonal Frequency Division Multiplexing Transceiver on a Real Time Platform developed by National Instruments. The various blocks needed to design a real time LTE based communications links are discussed. An experimental LTE-to-LTE interference analysis based on the Real Time Platform and the designed system is presented.M.S.Includes bibliographical referencesby Ajay Ramkumar Iye
Rational singularities of nested Hilbert schemes
Get PDFThe Hilbert scheme of points Hilb^n(S) of a smooth surface S is a well-studied parameter space, lying at the interface of algebraic geometry, commutative algebra, representation theory, combinatorics, and mathematical physics. The foundational result is a classical theorem of Fogarty, stating that Hilb^n(S) is a smooth variety of dimension 2n. In recent years there has been growing interest in a natural generalization of Hilb^n(S), the nested Hilbert scheme Hilb^(n1,n2)(S), which parametrizes nested pairs of zero-dimensional subschemes Z1 ⊇ Z2 of S with deg Zi = ni. In contrast to Fogarty’s theorem, Hilb^(n1,n2)(S) is almost always singular, and very little is known about its singularities. In this paper, we aim to advance the knowledge of the geometry of these nested Hilbert schemes. Work by Fogarty in the 70’s shows that Hilb(n,1)(S) is a normal Cohen–Macaulay variety, and Song more recently proved that it has rational singularities. In our main result, we prove that the nested Hilbert scheme Hilb(n,2)(S) has rational singularities. We employ an array of tools from commutative algebra to prove this theorem. Using Gröbner bases, we establish a connection between Hilb(n,2)(S) and a certain variety of matrices with an action of the general linear group. This variety of matrices plays a central role in our work, and we analyze it by various algebraic techniques, including the Kempf–Lascoux–Weyman technique of calculating syzygies, square-free Gröbner degenerations, and the Stanley–Reisner correspondence. Along the way, we also obtain results on classes of irreducible and reducible nested Hilbert schemes, dimension of singular loci, and F-singularities in positive characteristic
SupFigureII – Supplemental material for Evaluation of the volume-value relationship in hip fracture care using evidence-based thresholds
No full textSupplemental material, SupFigureII for Evaluation of the volume-value relationship in hip fracture care using evidence-based thresholds by Sergio M Navarro, William C Frankel, Heather S Haeberle, Damien G Billow and Prem N Ramkumar in HIP International</p
Supplementary_Figure_I – Supplemental material for Evaluation of the volume-value relationship in hip fracture care using evidence-based thresholds
No full textSupplemental material, Supplementary_Figure_I for Evaluation of the volume-value relationship in hip fracture care using evidence-based thresholds by Sergio M Navarro, William C Frankel, Heather S Haeberle, Damien G Billow and Prem N Ramkumar in HIP International</p
sj-pdf-1-ajs-10.1177_03635465211063901 – Supplemental material for Risk Factors for Failure After Osteochondral Allograft Transplantation of the Knee: A Systematic Review and Exploratory Meta-analysis
No full textSupplemental material, sj-pdf-1-ajs-10.1177_03635465211063901 for Risk Factors for Failure After Osteochondral Allograft Transplantation of the Knee: A Systematic Review and Exploratory Meta-analysis by Kyle N. Kunze, Joseph S. Manzi, Joshua Wright-Chisem, Prem Ramkumar, Benedict U. Nwachukwu and Riley J. Williams in The American Journal of Sports Medicine</p
sj-pdf-1-pie-10.1177_09544089221077661 - Supplemental material for Influence of rotation speeds on microstructure and mechanical properties of welded joints of friction stir welded AA2014-T6/AA6061-T6 alloys
No full textSupplemental material, sj-pdf-1-pie-10.1177_09544089221077661 for Influence of rotation speeds on microstructure and mechanical properties of welded joints of friction stir welded AA2014-T6/AA6061-T6 alloys by T Ramkumar, A Haiter Lenin, M Selva kumar, M Mohanraj, S Christopher Ezhil Singh and M Muruganandam in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p
Enhancement of tensile strength in AA 6061-T6 plates joined by gas tungsten arc welding using high entropy alloy filler sheet
No full textThis work has focused on enhancing the tensile strength of AA 6061-T6 plates by gas tungsten arc welding (GTAW) using an AA 1100-O sheet embedded with a high entropy alloy (HEA, Cr0.14Fe0.13Al0.26Cu0.11-Si0.25Zn0.11) as a filler metal. HEA filler sheets were prepared by accumulative roll bonding (ARB). The prepared (AA 1100-O)-HEA filler metal was used to join the AA 6061-T6 plates. Phase formation and microstructural evaluations were carried out using an x-ray diffractometer and advanced electron microscopy in the (AA 6061T6)-HEA weldment. The phase evaluation results revealed the presence of HEA with Al peaks and unveiled FCC phase formations and disappearance of the BCC phase owing to the incorporation of more FCC elements and less solid dissolution. The major FCC phase is attributed to the atomic radius mismatch among the incorporated metallic elements. The retention of the HEA phase after welding indicated thermal stability and sluggish diffusion behaviour. (AA 6061-T6)-10 wt.% HEA welded plates exhibited higher strength and plasticity due to the presence of nanocrystalline HEA, superior interfacial bonding between AA 6061-T6 and HEA elements, and the involvement of solid solution (178 MPa), dislocation (152 MPa), and grain boundary strengthening (27 MPa) towards the total strength (357 MPa).11Nsciescopu
Diffusion of eco-innovation through inter-firm network targeting: An agent-based model
No full textTo address increasingly urgent global environmental challenges, there is a need for rapid and widespread adoption of eco-innovations. Previous research has shown that targeting key initial adopters using network-based strategies is an effective way to increase the adoption and diffusion of innovations; however, these models have not specifically been applied to the diffusion of eco-innovations through inter-firm networks. Therefore, this paper develops an agent-based model that tests various network-based targeting strategies on generated inter- firm networks with different parameters to understand mechanisms that could boost and accelerate the adop-tion and diffusion of eco-innovations. The results show that targeting firms with high degree or high influence could more quickly diffuse incremental eco-innovations, while targeting neighbors of adopters is a better strategy for more radical eco-innovations with greater barriers to adoption. This has implications for policymakers, companies, and startups who wish to accelerate eco-innovation adoption and diffusion to create positive societal impacts
Evolution of microstructure and mechanical properties of [Cu-10Ni]-Si3N4 nanocomposites developed using mechanical alloying and spark plasma sintering
No full textThis study focused on the production of [Cu-10 Ni](x)-x wt% Si3N4 (x = 0, 3, 6, 9 and 12 wt%) nanocomposites through mechanical alloying followed by spark plasma sintering. An exhaustive exploration was carried out on the synthesised nanocrystalline/nanocomposite particles and sintered samples to study their structural characterisation and microstructural changes after 20 h of MA. The mechanical behaviour in terms of the compression test was carried out and correlated with the microstructural evaluations. The results indicated that the incorporation of Si3N4 nanoparticles decreased the matrix powder particle size considerably owing to the domination of fracturing mechanism. The results also showed that a higher strain hardening rate followed by the breaking up of the matrix powder particles occurred in the nanocomposite powders. The powder morphology of the nanocrystalline [Cu-10Ni] matrix ensured the uniform distribution of Si3N4 nanoparticles within it leading to the formation of dislocations in commensurate with the reinforcement addition. The sintered samples exhibited improved compression strength owing to the embedment of Si3N4 nanoparticles, strong bonding between the Si3N4 particles and the matrix, engendered dislocations and grain refinement. The ductility was examined and the strengthening mechanisms were computed for the deformed specimens. The results explained that the grain size, dislocation, and Orowan strengthening contributed more to the total strength and influenced the properties compared to other strengthening mechanisms. (C) 2021 Elsevier B.V. All rights reserved.11Nsciescopu
In-Vivo Characterization of S-cone Topography Across the Human Macula
No full textThesis (Ph.D.)--University of Washington, 2024Patterns of S-cone topography, the arrangement of short-wavelength sensitive photoreceptors in the retina, have long fascinated vision scientists. Many aspects of human S-cone topography are not well understood due to paucity of data. In this body of work, we examined S-cone topography from ROIs spanning the central ~1-12deg of the retina in two subjects. This comprises the largest dataset of human S-cone topography period, let alone within individuals. We developed novel approaches to characterize the semi-regular topography of S-cones, which led to the discovery of a novel pattern: that they are unlikely to be found within two concentric rings of cones surrounding S-cones. In addition, we found that S-cones are likely to have significantly far neighbors in the central retina (< 3 deg), and likely to have significantly near neighbors more peripherally. In total, this work provides a number of new analytic and simulation methods that show promise for the study of cone topography, and reveals robust insights into the patterns underlying human S-cone topography
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