Publication5

A series of Eu2+-activated barium orthosilicates (BaZnSiO4) were synthesized using a high-temperature solid-state reaction. A photoluminescence excitation study of Eu2+ shows a broad absorption band in the range of 270–450 nm, with multiple absorption peak maxima (310, 350 and 400 nm) due to 4f–5d electronic transition. The emission spectra of all the compositions show green color emission (in the spectral region 450–550 nm with a peak maximum at 502 nm and a shoulder at ~ 490 nm) with appropriate Comission Internationale de l'Eclairage (CIE) color coordinates. The two emission peaks are due to the presence of Eu2+ in two different Ba sites in the BaZnSiO4 host lattice. The energy transfers between the Eu2+ ions in BaZnSiO4 host are elucidated from the critical concentration quenching data based on the electronic multipolar interaction. All Eu2+-activated BaZnSiO4 phosphor materials can be efficiently excited in the ultraviolet (UV) to near UV-region (270–420 nm), making them attractive candidate as a green phosphor for solid state lighting–white light-emitting diodes.

This paper presents the dynamic modeling and performance control of a Web server hosted on a private cloud. The cloud hosting Web server is a variable capacity system with two control inputs: 1) the number of virtual machines (VMs), which is indicative of the capacity of the cloud, and 2) the admission control used for regulating workload. As the workload and the hosting conditions change frequently, the linear parameter-varying (LPV) framework is well suited to derive the model. For the hosted Web server, we obtain an multiple input multiple output (MIMO) LPV model with performance metrics such as the response time and the throughput, which is then converted to polytopic LPV form using tensor product transformation. Finally, we design a gain scheduled linear quadratic regulator controller for performance guarantees with optimal cost of VMs. The identification, validation, and control experiments are demonstrated on the open source Eucalyptus cloud platform. The HTTP requests are generated using customized synthetic workload generator tool.

Molecular doping of graphene is intriguing since the electronic and vibrational properties of graphene are not only determined by the interfacial charge transfer process, but they can also be influenced by adsorbate–graphene hybridization, adsorbate–adsorbate interactions, as well as Fermi-level pinning of the molecule. In this work, we investigate the change in vibrational properties of graphene induced by an organic electron acceptor molecule in the presence of intervening spacers of ultra-thin molybdenum disulphide (MoS2) of variable thickness, down to a single layer. Mechanically exfoliated single-layer graphene and few-layer MoS2 crystals are combined to form heterostructures, which are then subjected to molecular doping by means of an organic hole-dopant, 7,7,8,8-tetracyanoquinodimethane (TCNQ). Variations in Raman G-peak parameters are discussed in terms of molecular doping of graphen e, when the dopant:graphene separation is controllably increased. We show that dopant-separation dependent Fermi level variations of graphene cannot be completely accounted within a simple charge transfer model. The additional mechanisms relevant to the complex nature of molecular doping are discussed.

Chikungunya virus is a growing human pathogen transmitted by mosquito bite. It causes fever, chills, nausea, vomiting, joint pain, headache, and swelling in the joints. Its replication and propagation depend on the protease activity of the Chikungunya virus-nsP2 protein, which cleaves the nsP1234 polyprotein replication complex into individual functional units. The N-terminal segment of papain is structurally identical with the Chikungunya virus-nsP2 protease. Hence, molecular dynamics simulations were performed to compare molecular mechanism of these proteases. The Chikungunya virus-snP2 protease shows more conformational changes and adopts an alternate conformation. However, N-terminal segment of these two proteases has identical active site scaffold with the conserved catalytic diad. Hence, some of the non-peptide inhibitors of papain were used for induced fit docking at the active site of the nsP2 to assess the binding mode. In addition, the peptides that connect different domains/protein in Chikungunya virus poly-protein were also subjected for docking. The overall results suggest that the active site scaffold is the same in both the proteases and a possibility exists to experimentally assess the efficacy of some of the papain inhibitors to inhibit the Chikungunya virus-nsP2.

We report the dynamical migration behavior of rigid polystyrene microparticles at an interface of co-flowing streams of primary CP1 (aqueous) and secondary CP2 (oils) immiscible phases at low Reynolds numbers (Re) in a microchannel. The microparticles initially suspended in the CP1 either continue to flow in the bulk CP1 or migrate across the interface into CP2, when the stream width of the CP1 approaches the diameter of the microparticles. Experiments were performed with different secondary phases and it is found that the migration criterion depends on the sign of the spreading parameter S and the presence of surfactant at the interface. To substantiate the migration criterion, experiments were also carried out by suspending the microparticles in CP2 (oil phase). Our study reveals that in case of aqueous-silicone oil combination, the microparticles get attached to the interface since S<0 and the three phase contact angle, θ>90°. For complete detachment of microparticles from the interface into the secondary phase, additional energy ΔG is needed. We discuss the role of interfacial perturbation, which causes detachment of microparticles from the interface. In case of mineral and olive oils, the surfactants present at the interface prevents attachment of the microparticles to the interface due to the repulsive disjoining pressure. Finally, using a aqueous-silicone oil system, we demonstrate size based sorting of microparticles of size 25 μm and 15 μm respectively from that of 15 μm and 10 μm and study the variation of separation efficiency η with the ratio of the width of the aqueous stream to the diameter of the microparticles ρ.