9,015 research outputs found
Probing Spin-Charge Relation by Magnetoconductance in One-Dimensional Polymer Nanofibers
Polymer nanofibers are one-dimensional organic hydrocarbon systems containing
conducting polymers where the non-linear local excitations such as solitons,
polarons and bipolarons formed by the electron-phonon interaction were
predicted. Magnetoconductance (MC) can simultaneously probe both the spin and
charge of these mobile species and identify the effects of electron-electron
interactions on these nonlinear excitations. Here we report our observations of
a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI)
and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is
present in PANI and PT. The universal scaling behavior and the zero (finite) MC
in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between
spinless charged solitons (interacting polarons which carry both spin and
charge)
Quantum beats in the electric-field quenching of metastable hydrogen
The strong field-induced quantum beats observed in beam-foil studies of Ly- alpha radiation are obtained in a conventional metastable-hydrogen quenching experiment. The phase relation between the Stark shifted 2s 1/2- 2p 1/2 Lamb-shift oscillations and the much more rapid 2s 1-2p 3/2 fine-structure oscillations depends on the detailed way in which the quenching field is switched on. Apart from a phaseshift, the results agree with a non-perturbative theoretical calculation which assumes that the field is applied suddenly. Various frequency components of the time-dependent radiation intensity are identified with specific hyperfine transitions or groups of transitions. No adjustable parameters are used for the initial state amplitudes
Correlated multiplexity and connectivity of multiplex random networks
Nodes in a complex networked system often engage in more than one type of
interactions among them; they form a multiplex network with multiple types of
links. In real-world complex systems, a node's degree for one type of links and
that for the other are not randomly distributed but correlated, which we term
correlated multiplexity. In this paper we study a simple model of multiplex
random networks and demonstrate that the correlated multiplexity can
drastically affect the properties of giant component in the network.
Specifically, when the degrees of a node for different interactions in a duplex
Erdos-Renyi network are maximally correlated, the network contains the giant
component for any nonzero link densities. In contrast, when the degrees of a
node are maximally anti-correlated, the emergence of giant component is
significantly delayed, yet the entire network becomes connected into a single
component at a finite link density. We also discuss the mixing patterns and the
cases with imperfect correlated multiplexity.Comment: Revised version, 12 pages, 6 figure
Nanofiltration of aerobically-treated palm oil mill effluent: Characterization of the size of colour compounds using synthetic dyes and polyethylene glycols
Membrane-based separation is one of the emerging technologies that have garnered significant interest in recent years for the treatment process of palm oil mill effluent (POME). As documented in the literature, different types of membrane processes such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were used for the POME treatment and the efficiency of separation varied depending on the membrane properties. Unlike the previous works that used membranes to treat POME, the main focus of this current work is to utilize NF membrane to characterize the size of colour compounds in the aerobically-treated POME (AT-POME). Two different markers, i.e., synthetic dyes and polyethylene glycols (PEGs) with molecular weight (MW) in the range of 200-1000 g/mol were used to characterize the colour compounds in the AT-POME. Results showed that dyes are more suitable compared to PEGs for the characterization because dyes possessed negative charge similar as the colour compounds in the AT-POME. By using dyes as the markers, it was found that the size of the colour compounds in the AT-POME was at MW of 300-400 g/mol. Precise determination of the size of colour compounds in the AT-POME is of importance as it could provide useful information on the selection of ideal membrane properties (in particular pore size or molecular weight cut-off) to achieve complete solute separation
Anti-fouling double-skinned forward osmosis membrane with zwitterionic brush for oily wastewater treatment
Despite its attractive features for energy saving separation, the performance of forward osmosis (FO) has been restricted by internal concentration polarization and fast fouling propensity that occur in the membrane sublayer. These problems have significantly affected the membrane performance when treating highly contaminated oily wastewater. In this study, a novel double-skinned FO membrane with excellent anti-fouling properties has been developed for emulsified oil-water treatment. The double-skinned FO membrane comprises a fully porous sublayer sandwiched between a highly dense polyamide (PA) layer for salt rejection and a fairly loose dense bottom zwitterionic layer for emulsified oil particle removal. The top dense PA layer was synthesized via interfacial polymerization meanwhile the bottom layer was made up of a zwitterionic polyelectrolyte brush-(poly(3-(N-2-methacryloxyethyl-N,N-dimethyl) ammonatopropanesultone), abbreviated as PMAPS layer. The resultant double-skinned membrane exhibited a high water flux of 13.7 ± 0.3 L/m2.h and reverse salt transport of 1.6 ± 0.2 g/m2.h under FO mode using 2 M NaCl as the draw solution and emulsified oily solution as the feed. The double-skinned membrane outperforms the single-skinned membrane with much lower fouling propensity for emulsified oil-water separation
Supergravity loop contributions to brane world supersymmetry breaking
We compute the supergravity loop contributions to the visible sector scalar
masses in the simplest 5D `brane-world' model. Supersymmetry is assumed to be
broken away from the visible brane and the contributions are UV finite due to
5D locality. We perform the calculation with N = 1 supergraphs, using a
formulation of 5D supergravity in terms of N = 1 superfields. We compute
contributions to the 4D effective action that determine the visible scalar
masses, and we find that the mass-squared terms are negative.Comment: 12 pages, LaTeX 2
Self-similar disk packings as model spatial scale-free networks
The network of contacts in space-filling disk packings, such as the
Apollonian packing, are examined. These networks provide an interesting example
of spatial scale-free networks, where the topology reflects the broad
distribution of disk areas. A wide variety of topological and spatial
properties of these systems are characterized. Their potential as models for
networks of connected minima on energy landscapes is discussed.Comment: 13 pages, 12 figures; some bugs fixed and further discussion of
higher-dimensional packing
Fluctuation-driven dynamics of the Internet topology
We study the dynamics of the Internet topology based on the empirical data on
the level of the autonomous systems. It is found that the fluctuations
occurring in the stochastic process of connecting and disconnecting edges are
important features of the Internet dynamics. The network's overall growth can
be described approximately by a single characteristic degree growth rate
and the fluctuation strength , together with the vertex growth rate . A
stochastic model which incorporate these values and an adaptation rule newly
introduced reproduces several features of the real Internet topology such as
the correlations between the degrees of different vertices.Comment: Final version appeared in Phys. Rev. Let
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