Intensity-Dependent Enhancement of Saturable Absorption in PbS-Au4 Nanohybrid Composites: Evidence for Resonant Energy Transfer by Auger Recombination

Intensity-dependent enhancement of saturable absorption in a film of PbS-Au4 nanohybrid composites has been observed by femtosecond time-resolved transient absorption measurement at 780 nm. The nonlinear absorption coefficient of saturable absorption in PbS-Au4 nanohybrid composites is found to be dependent on excitation irradiance and it is determined to be -2.9 cm/GW at 78 GW/cm2, an enhancement of nearly fourfold in comparison with that of pure PbS quantum dots (QDs). The enhancement is attributed to excitation of surface plasmon by resonant energy transfer between PbS QDs and Au nanoparticles through Auger recombination.Comment: 14 pages, 3 figures. Accepted in Appl. Phys. Lett. (2008

Nonlinear optical properties of mono-functional 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid /polymer composites

By using nanosecond laser pulses at 532-nm wavelength, we have studied the nonlinear optical properties of composites which consist of mono-functional 1,2-dihydro-1,2-methanofullerene[60]-61-carboxylic acid (FCA) and poly(styrene-co-4-vinylpyridine). The optical limiting performance of FCA itself is poorer than that of its parent C60, while FCA incorporated with polystyrene shows better optical limiting responses, with the limiting threshold reduced by about 35%. In addition, the FCA gives slightly stronger photoluminescence emission than that of both C60 and FCA/polymer composites. The possible sources for the improvement in the optical limiting are discussed.Comment: 14 pages, 4 figures, To appear in Chem. Phys. Let

Observation of Saturable and Reverse Saturable Absorption at Longitudinal Surface Plasmon Resonance in Gold Nanorods

Saturable and reverse saturable absorption at longitudinal surface plasmon resonance (SPR) in gold nanorods (Au NRs) have been observed using Z-scan and transient absorption techniques with femtosecond laser pulses. At lower excitation irradiances, the wavelength dispersion of saturable absorption has been determined near the longitudinal mode of SPR with a recovery time determined to be a few ten picoseconds on the SPR resonance. With higher excitation irradiances, reverse saturable absorption occurs and becomes dominant. The underlying mechanisms are discussed. Such reversible saturable absorption makes Au NRs an ideal candidate for optical limiting applications.Comment: 13 pages, 3 figure

Enhanced roughness of lipid membranes caused by external electric fields

The behavior of lipid membranes in the presence of an external electric field is studied and used to examine the influence of such fields on membrane parameters such as roughness and show that for a micro sized membrane, roughness grows as the field increases. The dependence of bending rigidity on the electric field is also studied and an estimation of thickness of the accumulated charges around lipid membranes in a free-salt solution is presented.Comment: 9 pages, 6 figures, to appear in Computational Materials Scienc

Nonlinear optics and optical limiting properties of multifunctional fullerenol/polymer composite

The nonlinear optics and optical limiting properties of materials based on multifunctional fullerenol and poly(styrene-co-4-vinylpyridine) matrix were studied using 7 ns pulses of nanosecond laser operating at 532 nm wavelength. The observed imaginary and real parts of third order susceptibility of the fullerenol/polymer composite are found to be lower than that of its parent C60. The optical limiting performances of fullerenol and fullerenol incorporated with poly(styrene-co-4-vinylpyridine) have been proved to be poorer than that of C60 due to their higher limiting thresholds. Concentration dependence of poly(styrene-co-4-vinylpyridine) containing 32 mol% has been mainly contributed to the optical limiting performance of fullerenol.Comment: 23 pages, 9 figures, presented in ISMOA-2002, Bandung, Indonesia. Submitted to J. Nonlinear Opt. Phys. (December 2002

Deppining of a Superfluid Vortex Inside a Circular Defect

In this work we study the process of depinning of a quantum of circulation trapped inside a disk by an applied two dimensional superflow. We use the Gross-Pitaevskii model to describe the neutral superfluid. The collective coordinate dynamics is derived directly from the condensate equation of motion, the nonlinear Schroedinger equation, and it is used to obtain an expression for the critical velocity as a function of the defect radius. This expression is compared with a numerical result obtained from the time independent nonlinear Schroedinger equation. Below the critical velocity, we obtain the dependence of the semiclassical nucleation rate with the flow velocity at infinity. Above the critical velocity, the classical vortex depinning is illustrated with a numerical simulation of the time dependent nonlinear Schroedinger equation.Comment: 8 pages, 5 figures, uses revtex and epsf.st

Multi-omic data integration elucidates Synechococcus adaptation mechanisms to fluctuations in light intensity and salinity

Synechococcus sp. PCC 7002 is a fast-growing cyanobacterium which flourishes in freshwater and marine environments, owing to its ability to tolerate high light intensity and a wide range of salinities. Harnessing the properties of cyanobacteria and understanding their metabolic efficiency has become an imperative goal in recent years owing to their potential to serve as biocatalysts for the production of renewable biofuels. To improve characterisation of metabolic networks, genome-scale models of metabolism can be integrated with multi-omic data to provide a more accurate representation of metabolic capability and refine phenotypic predictions. In this work, a heuristic pipeline is constructed for analysing a genome-scale metabolic model of Synechococcus sp. PCC 7002, which utilises flux balance analysis across multiple layers to observe flux response between conditions across four key pathways. Across various conditions, the detection of significant patterns and mechanisms to cope with fluctuations in light intensity and salinity provides insights into the maintenance of metabolic efficiency

Financial crises and the attainment of the SDGs: an adjusted multidimensional poverty approach

This paper analyses the impact of financial crises on the Sustainable Development Goal of eradicating poverty. To do so, we develop an adjusted Multidimensional Poverty Framework (MPF) that includes 15 indicators that span across key poverty aspects related to income, basic needs, health, education and the environment. We then use an econometric model that allows us to examine the impact of financial crises on these indicators in 150 countries over the period 1980–2015. Our analysis produces new estimates on the impact of financial crises on poverty’s multiple social, economic and environmental aspects and equally important captures dynamic linkages between these aspects. Thus, we offer a better understanding of the potential impact of current debt dynamics on Multidimensional Poverty and demonstrate the need to move beyond the boundaries of SDG1, if we are to meet the target of eradicating poverty. Our results indicate that the current financial distress experienced by many low-income countries may reverse the progress that has been made hitherto in reducing poverty. We find that financial crises are associated with an approximately 10% increase of extreme poor in low-income countries. The impact is even stronger in some other poverty aspects. For instance, crises are associated with an average decrease of government spending in education by 17.72% in low-income countries. The dynamic linkages between most of the Multidimensional Poverty indicators, warn of a negative domino effect on a number of SDGs related to poverty, if there is a financial crisis shock. To pre-empt such a domino effect, the specific SDG target 17.4 on attaining long-term debt sustainability through coordinated policies plays a key role and requires urgent attention by the international community

Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland

Correct interpretation of soft-bodied fossils relies on a thorough understanding of their taphonomy. While the focus has often been on the primary roles of decay and early diagenesis, the impacts of deeper burial and metamorphism on fossil preservation are less well understood. We document a sequence of late-stage mineral replacements in panarthropod fossils from the Sirius Passet Lagerstätte (North Greenland), an important early Cambrian Burgess Shale–type (BST) biota. Muscle and gut diverticula were initially stabilized by early diagenetic apatite, prior to being pervasively replaced by quartz and then subordinate chlorite, muscovite, and chloritoid during very low- to low-grade metamorphism. Each new mineral replicates the soft tissues with different precision and occurs in particular anatomical regions, imposing strong biases on the biological information retained. Muscovite and chloritoid largely obliterate the tissues’ original detail, suggesting that aluminum-rich protoliths may have least potential for conserving mineralized soft tissues in metamorphism. Overall, the fossils exhibit a marked shift toward mineralogical equilibration with the matrix, obscuring primary taphonomic modes. Sequential replacement of the phosphatized soft tissues released phosphorus to form new accessory monazite (and apatite and xenotime), whose presence in other BST biotas might signal the prior, more widespread, occurrence of this primary mode of preservation. Our results provide critical context for interpreting the Sirius Passet biota and for identifying late-stage overprints in other biotas