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Manjceevan A.,Sri Lanka Institute of Fundamental Studies | Bandara J.,Sri Lanka Institute of Fundamental Studies
Electrochimica Acta | Year: 2017

Fabrication of low cost and high catalytic active counter electrode (CE) for quantum dot sensitized solar cells is one of the dynamic ways to enhance the performance of quantum dot solar cell. In this investigation, different CE materials such as copper sulfide (Cu2S), cobalt sulfide (CoS) and nickel sulfide (NiS) were deposited on fluorine doped tinoxide (FTO) glass and brass plate by single step electrophoretic deposition technique and solar cell performance and stability of three different CEs were tested. Electrochemical deposition parameters were optimized for the optimization of CEs performance. Electrical properties of Cu2S, CoS and NiS CEs were investigated by electrochemical impedance spectroscopy and electrical properties were compared with the observed solar cell performances and stability. Of the tested CEs materials, enhanced solar cell performance was observed with Cu2S CE than the CoS or NiS CEs while brass substrae was found to be a better substrate than FTO for these CE materials. The optimized Cu2S/brass plate CE showed current density of (Jsc) 17.9 mA.cm−2, open circuit voltage of (Voc) 494.5 mV, fill factor of (FF) 59.0% and efficiency of 5.2% with the solar cell fabricated with PbS/CdS q-dot anode. While Cu2S/FTO glass plate CE showed Jsc of 16.1 mA.cm−2, Voc of 489.4 mV, FF of 52.9% and efficiency of 4.2% of with the same q-dot anode. A higher electrocatalytic activity together with the lower charge transfer resistance (Rct) and good inter-connected Cu2S particles on brass electrodes were found to be the major CE properties that decides the performance of CE. © 2017 Elsevier Ltd

Seneviratne G.,Sri Lanka Institute of Fundamental Studies | Kulasooriya S.A.,Sri Lanka Institute of Fundamental Studies
Agriculture, Ecosystems and Environment | Year: 2013

It has been reported that collapse of soil microbial diversity, mainly due chemical inputs leads to degradation of conventional agroecosystems. Indirect methods related to manipulation of plant and animal components in the ecosystems have been currently practised to reinstate the microbial diversity. However, those methods are laborious and time-consuming, and hence less efficient. Also, there are limits to those management methods due to ever increasing global food demand, particularly in tropics. Therefore, we have to look for methods that sustain productivity of large-scale conventional croplands even with continuous mono-cropping. This article reports that direct soil application of developed microbial communities in biofilm mode increases microbial diversity in the agroecosystems through breaking dormancy of microbial seed bank. That contributes to strengthen biodiversity-ecosystem functioning relationship, which leads to agroecosystem sustainability. © 2012 Elsevier B.V.

Nanayakkara A.,Sri Lanka Institute of Fundamental Studies
Journal of Physics A: Mathematical and Theoretical | Year: 2012

Dynamical tunneling occurs when a particle tunnels between two distinct classically trapped periodic regions of classical phase space that are not separated by a potential barrier. Although the dynamical tunneling has been observed in many multi-dimensional Hamiltonian systems, it has not been observed in 1D systems described by a single potential. In this paper, we show that classical trajectories of real potentials such as V 1(x) = x 4 exhibit dynamical tunneling-like behavior when energy or time is complex. It was found that the doubly periodic nature of the Jacobian elliptic functions is responsible for this dynamical tunneling-like behavior. The time spent in one region by the tunneling trajectory before crossing over to the other is found to be proportional to , where total energy E = E 0 + iΔE with E 0 < 0. Furthermore, we demonstrate that classical trajectories of the non-Hermitian system V 2(x) = x 4 + (1 + i)x show evidence of dynamical tunneling even for real energies. The role of complex time in dynamical tunneling is discussed. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to Quantum physics with non-Hermitian operators. © 2012 IOP Publishing Ltd.

Wijeratne K.,Sri Lanka Institute of Fundamental Studies | Bandara J.,Sri Lanka Institute of Fundamental Studies
Electrochimica Acta | Year: 2014

Though one-dimensional (1-D) ZnO nanrods are promising transport electron transport material in the photoanode of Dye Sensitized Solar Cells (DSSC), 1-D ZnO nanorod based DSSCs exhibit poor energy conversion efficiencies. In this study, DSSCs were fabricated with 1-D ZnO nanorods having different aspect ratio and the dependence of solar cell performance on aspect ratio of ZnO nanorods was investigated. Photoanodes fabricated with different 1-D ZnO nanorods having aspect ratios of 4.4, 5.4, 5.8, 6.8 and 7.6 showed increasing solar cell performance with the increase of aspect ratio where 2.1 and 4.7% light conversion efficiencies were observed respectively for the lowest and highest aspect ratio of 1-D ZnO nanostructures. We study the electrical and operational differences between DSSC made with ZnO nanostructures with different aspect ratio. Electrochemical impedance spectroscopy (EIS) is used to quantify the aspect ratio depended electron transport properties, charge recombination, life-time and charge diffusion lengths of excited electrons in 1D ZnO nanorods and electron transport properties are correlated to the observed cell performance. In addition, effect of aspect ratio of ZnO nanorods on dye loading amount and light scattering properties were also investigated. © 2014 Elsevier Ltd.

Benjamin S.P.,Sri Lanka Institute of Fundamental Studies | Benjamin S.P.,Smithsonian Institution
Zootaxa | Year: 2011

The higher-level phylogenetic relationships of crab spiders (Thomisidae) are studied from morphological data. 33 taxa are coded for 74 characters (53 binary and 21 multistate). Several analyses using equal, successive and implied weights were carried out. The most parsimonious tree obtained by analysis with successive and implied weights is put forward as the preferred hypothesis of thomisid relationships (length 222 steps, CI 0.74, RI 0.83). Thomisidae emerge monophyletic in all analyses, supported by four unambiguous synapomorphies. It is now apparent that thomisid taxa have been mostly defined on the basis of plesiomorphic character states. A number of taxonomic changes, including the description of new taxa are proposed and the evolution of diverse behaviors of thomisids is studied in light of the new phylogenetic result. Color change behavior evolved once within the family, but eye arrangement patterns of the median ocular quadrangle, thought to be diagnostic for many genera, evolved as much as 10 times independently. The following new species are described: Borboropactus nyerere sp. nov.,Cebrenninus srivijaya sp. nov., Geraesta lehtineni sp. nov. and Geraesta mkwawa sp. nov. The following new generic synonymies are proposed: Bucranium O. P.-Cambridge, 1881 = Aphantochilus O. P.-Cambridge, 1870; Sanmenia Song and Kim, 1992 = Pharta Thorell, 1891 and Cupa Strand, 1906 = Epidius Thorell, 1877. The following species are synonymized: Regillus divergens Hogg, 1914 and Borboropactus hainanus Song, 1993 = Borboropactus bituberculatus Simon, 1884 syn. nov., Epidius ganxiensis (Yin, Peng & Kim, 1999) = Epidius rubropictus Simon, 1909 syn. nov., Geraesta bilobata Simon, 1897 = Geraesta hirta Simon, 1889 syn. nov., Sanmenia kohi Ono, 1995 = Pharta bimaculata Thorell, 1891 syn. nov. and Sanmenia zhengi (Ono & Song, 1986) = Pharta brevipalpus (Simon, 1903) syn. nov. The following new combinations are proposed: Aphantochilus taurifrons (O. P.-Cambridge, 1881) comb. nov., Epidius typicus (Bösenberg & Strand, 1906) comb. nov., Pharta brevipalpus (Simon, 1903) comb. nov., Pharta gongshan (Yang, Zhu and Song, 2006) comb. nov., Pharta nigra (Tang, Griswold & Peng, 2009) comb. nov. and Pharta tengchong (Tang, Griswold & Yin, 2009) comb. nov. © 2011 Magnolia Press.

Seneviratne G.,Sri Lanka Institute of Fundamental Studies
Agriculture, Ecosystems and Environment | Year: 2015

Sustainability of natural and agro ecosystems is governed mainly by soil processes. In these, contributions of the biotic or living constituents are much important. The biotic part is represented by soil food web. Here, I argue that the sustainability of the ecosystems is an outcome of chemical signaling in the food web. Then, I show that it is the microbes living mainly endophytically and in the soil, including fauna, which contribute to ecosystem balance through signaling in complex network interactions. Sustenance of edaphic or soil ecosystems collapses when the signaling is retarded due to human impact and global change. This issue can only be addressed by manipulating soil microbes. I introduce a new term edaphic ecosystem signal transduction (EST), which can summarize the concept explained in this article. © 2015 Elsevier B.V.

Nanayakkara A.,Sri Lanka Institute of Fundamental Studies
Canadian Journal of Physics | Year: 2012

Analytic semiclassical energy expansions of nonpolynomial oscillator (NPO) potentials V(x) = x 2N + (λx m1)/(1 + gx m2) are obtained for arbitrary positive integers N, m 1, and m 2, and the real parameters λ and g using the asymptotic energy expansion (AEE) method. Because the AEE method has been previously developed only for polynomial potentials, the method is extended with new types of recurrence relations. It is then applied to the preceding general NPO to obtain expressions for quantum action variable J in terms of E and the parameters of the potential. These expansions are power series in energy and the coefficients of the series contain parameters λ and g explicitly. To avoid the singularities in the potential we only consider the cases where both λ and g are non-negative at the same time. Using the AEE expressions, it is shown that, for certain classes of NPOs, if potentials have the same N, and the same m 1 - m 2 or m 1 - 2m 2 then they have the same asymptotic eigenspectra. It was also shown that for certain cases, both λ and -λ as well as g and -g will produce the same asymptotic energy spectra. Analytic expressions are also derived for asymptotic level spacings of general NPOs in terms of λ and g. © 2012 Published by NRC Research Press.

Nanayakkara A.,Sri Lanka Institute of Fundamental Studies
Canadian Journal of Physics | Year: 2013

In recent years, much research has been carried out on extending both quantum mechanics and classical mechanics into the complex domain by making parameters of real hermitian Hamiltonians or total energy of the system complex. In this paper we investigate the effects of complex time on periodic and nonperiodic trajectories of both hermitian and nonhermitian one-dimensional classical Hamiltonian systems. Most of the periodic classical trajectories of real hermitian systems turn into nonperiodic and open when the energy or the parameters of the potential become complex. We show that when time is taken as a complex quantity with a specific fixed phase angle or as a specific complex function, nonperiodic trajectories become periodic and closed. Furthermore, we show that real hermitian systems, such as H = p2/2m + x4 + bx3 + cx2 + dx (b, c, and d are real quantities) possess classical periodic trajectories for real energies even when time is complex (i.e., t = treiτ). It was found that there is a discrete set of τ values for which the trajectories of the preceding system are closed and periodic and periods associated with them form a countably infinite set. © 2013 Published by NRC Research Press.

Jaiswal R.,Jacobs University Bremen | Jayasinghe L.,Sri Lanka Institute of Fundamental Studies | Kuhnert N.,Jacobs University Bremen
Journal of Mass Spectrometry | Year: 2012

The proanthocyanidins of the leaves of 16 taxa of the Rhododendron genus (Ericaceae) [Rhododendron 'Catawbiense Grandiflorum', Rhododendron 'Cunningham's White', Rhododendron smirnowii Trautv., Rhododendron calophytum Franch., Rhododendron dichroanthum ssp. scyphocalyx (Balf. f. & Forrest) Cowan, Rhododendron micranthum Turcz., Rhododendron praevernum Hutch., Rhododendron ungernii Trautv., Rhododendron kaempferi Planch., Rhododendron degronianum ssp. heptamerum var. hondoense (Nakai) H. Hara, Rhododendron fortunei Lindl., Rhododendron ponticum L., Rhododendron galactinum Balf. f. ex Tagg., Rhododendron oreotrephes W. W. Sm., Rhododendron brachycarpum ssp. brachycarpum D. Don ex G. Don, and Rhododendron insigne Hemsl. & E. H. Wilson] were investigated qualitatively by liquid chromatography-mass spectrometry in series. Twenty-nine dimeric proanthocyanidins based on (epi)catechin and (epi)gallocatechin were detected and characterized on the basis of their unique fragmentation pattern in the negative ion mode tandem mass spectrometry spectra. All of them were extracted for the first time from these sources, and ten of them were not reported previously in nature. The position of the galloyl residue was assigned on the basis of the retro-Diels-Alder fragmentation and the dehydrated retro-Diels-Alder fragmentation; it resulted from the loss of gallic acid as a neutral loss in the negative ion mode. Furthermore, four caffeoylquinic acids, six p-coumaroylquinic acids, epigallocatechin, gallocatechin, catechin, epicatechin, epigallocatechin gallate, catechin gallate, epicatechin gallate, gallocatechin gallate, two quercetin-O-hexosides, quercetin-O-galloyl-hexoside, quercetin-O-pentoside, quercetin-O-rhamnoside, quercetin-O-pentoside-O-hexoside, quercetin-O-rhamnoside-O-hexoside, quercetin-O-feruloyl-hexoside, quercetin-O-(p-hydroxy)benzoyl-hexoside, taxifolin-O-pentoside, myricetin-O-rhamnoside, two myricetin-O-pentosides, three myricetin-O-hexosides, and two myricetin-O-galloyl-hexosides were detected and shown to possess characteristic tandem mass spectrometry spectra and were tentatively assigned on the basis of their retention time. Copyright © 2012 John Wiley & Sons, Ltd.

Wijeratne K.,Sri Lanka Institute of Fundamental Studies | Akilavasan J.,Sri Lanka Institute of Fundamental Studies | Thelakkat M.,University of Bayreuth | Bandara J.,Sri Lanka Institute of Fundamental Studies
Electrochimica Acta | Year: 2012

Efficiency of dye-sensitized solar cells (DSSC) fabricated with pristine SnO 2 nanocrystals was reported to be less superior compared to DSSC based on mesoporous TiO 2 nanoparticles though both oxides have comparable electrical and surface properties. Owing to inherent high charge recombination properties of SnO 2 nanoparticles, photoanode fabricated with SnO 2 nanoparticles resulting in unexpected low open circuit voltage (V oc) and fill factor (FF). To overcome inherent charge recombination in SnO 2, we investigated pristine SnO 2 nanorods and showed enhanced V oc, FF and overall conversion efficiency (η) for SnO 2 nanorods. The photoanode made of SnO 2 nanorods yields nearly a 2-fold improvement in fill factor, 5 fold increases in η and a greater than 2-fold increase in short-circuit current density with a moderate increase in open-circuit photovoltage. The effects appear to arise primarily from longer electron lifetimes and reduced charge recombination of SnO 2 nanorod based solar cells compared to that of SnO 2 particles owing to 1-D nature of SnO 2 nanorod which were evaluated by open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) methods. © 2012 Elsevier Ltd.

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