481 research outputs found
Modeling electrodialysis and a photochemical process for their integration in saline wastewater treatment.
Oxidation processes can be used to treat industrial wastewater containing non-biodegradable organic compounds. However, the presence of dissolved salts may inhibit or retard the treatment process. In this study, wastewater desalination by electrodialysis (ED) associated with an advanced oxidation process (photo-Fenton) was applied to an aqueous NaCl solution containing phenol. The influence of process variables on the demineralization factor was investigated for ED in pilot scale and a correlation was obtained between the phenol, salt and water fluxes with the driving force. The oxidation process was investigated in a laboratory batch reactor and a model based on artificial neural networks was developed by fitting the experimental data describing the reaction rate as a function of the input variables. With the experimental parameters of both processes, a dynamic model was developed for ED and a continuous model, using a plug flow reactor approach, for the oxidation process. Finally, the hybrid model simulation could validate different scenarios of the integrated system and can be used for process optimization
Macroscopic Symmetry Group Describes Josephson Tunneling in Twinned Crystals
A macroscopic symmetry group describing the superconducting state of an
orthorhombically twinned crystal of YBCO is introduced. This macroscopic
symmetry group is different for different symmetries of twin boundaries.
Josephson tunneling experiments performed on twinned crystals of YBCO determine
this macroscopic symmetry group and hence determine the twin boundary symmetry
(but do not experimentally determine whether the microscopic order parameter is
primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in
YBCO is the stability of vortices containing one half an elementary flux
quantum at the intersection of a twin boundary and certain grain boundaries.Comment: 6 pages, to be published in the Proceedings of the MOS96 Conference
in the Journal of Low Temperature Physic
Larval dispersal in a changing ocean with an emphasis on upwelling regions
Dispersal of benthic species in the sea is mediated primarily through small, vulnerable larvae that must survive minutes to months as members of the plankton community while being transported by strong, dynamic currents. As climate change alters ocean conditions, the dispersal of these larvae will be affected, with pervasive ecological and evolutionary consequences. We review the impacts of oceanic changes on larval transport, physiology, and behavior. We then discuss the implications for population connectivity and recruitment and evaluate life history strategies that will affect susceptibility to the effects of climate change on their dispersal patterns, with implications for understanding selective regimes in a future ocean. We find that physical oceanographic changes will impact dispersal by transporting larvae in different directions or inhibiting their movements while changing environmental factors, such as temperature, pH, salinity, oxygen, ultraviolet radiation, and turbidity, will affect the survival of larvae and alter their behavior. Reduced dispersal distance may make local adaptation more likely in well-connected populations with high genetic variation while reduced dispersal success will lower recruitment with implications for fishery stocks. Increased dispersal may spur adaptation by increasing genetic diversity among previously disconnected populations as well as increasing the likelihood of range expansions. We hypothesize that species with planktotrophic (feeding), calcifying, or weakly swimming larvae with specialized adult habitats will be most affected by climate change. We also propose that the adaptive value of retentive larval behaviors may decrease where transport trajectories follow changing climate envelopes and increase where transport trajectories drive larvae toward increasingly unsuitable conditions. Our holistic framework, combined with knowledge of regional ocean conditions and larval traits, can be used to produce powerful predictions of expected impacts on larval dispersal as well as the consequences for connectivity, range expansion, or recruitment. Based on our findings, we recommend that future studies take a holistic view of dispersal incorporating biological and oceanographic impacts of climate change rather than solely focusing on oceanography or physiology. Genetic and paleontological techniques can be used to examine evolutionary impacts of altered dispersal in a future ocean, while museum collections and expedition records can inform modern-day range shifts
Conformational Mechanics of Polymer Adsorption Transitions at Attractive Substrates
Conformational phases of a semiflexible off-lattice homopolymer model near an
attractive substrate are investigated by means of multicanonical computer
simulations. In our polymer-substrate model, nonbonded pairs of monomers as
well as monomers and the substrate interact via attractive van der Waals
forces. To characterize conformational phases of this hybrid system, we analyze
thermal fluctuations of energetic and structural quantities, as well as
adequate docking parameters. Introducing a solvent parameter related to the
strength of the surface attraction, we construct and discuss the
solubility-temperature phase diagram. Apart from the main phases of adsorbed
and desorbed conformations, we identify several other phase transitions such as
the freezing transition between energy-dominated crystalline low-temperature
structures and globular entropy-dominated conformations.Comment: 13 pages, 15 figure
Probing structural relaxation in complex fluids by critical fluctuations
Complex fluids, such as polymer solutions and blends, colloids and gels, are
of growing interest in fundamental and applied soft-condensed-matter science. A
common feature of all such systems is the presence of a mesoscopic structural
length scale intermediate between atomic and macroscopic scales. This
mesoscopic structure of complex fluids is often fragile and sensitive to
external perturbations. Complex fluids are frequently viscoelastic (showing a
combination of viscous and elastic behaviour) with their dynamic response
depending on the time and length scales. Recently, non-invasive methods to
infer the rheological response of complex fluids have gained popularity through
the technique of microrheology, where the diffusion of probe spheres in a
viscoelastic fluid is monitored with the aid of light scattering or microscopy.
Here we propose an alternative to traditional microrheology that does not
require doping of probe particles in the fluid (which can sometimes drastically
alter the molecular environment). Instead, our proposed method makes use of the
phenomenon of "avoided crossing" between modes associated with the structural
relaxation and critical fluctuations that are spontaneously generated in the
system.Comment: 4 pages, 4 figure
Josephson tunneling in high- superconductors
This article describes the Josephson tunneling from time-reversal
symmetry-breaking states and compares it with that from time-reversal invariant
states for both twinned and untwinned crystals and for both -axis and
basal-plane currents, in a model for orthorhombic YBCO. A macroscopic
invariance group describing the superconducting state of a twinned crystal is
introduced and shown to provide a useful framework for the discussion of the
results for twinned crystals. In addition, a ring geometry, which allows
-wave and -wave superconductivity in a tetragonal
superconductor to be distinguished on the basis of symmetry arguments only, is
proposed and analyzed. Finally, an appendix gives details of the experimental
Josephson tunneling evidence for a superconducting state of orthorhombic
symmetry in YBCO.Comment: Latex File, 18 pages, 6 Postscript figures, submitted to Phys. Rev.
Molecular Valves for Controlling Gas Phase Transport Made from Discrete Angstrom-Sized Pores in Graphene
An ability to precisely regulate the quantity and location of molecular flux
is of value in applications such as nanoscale 3D printing, catalysis, and
sensor design. Barrier materials containing pores with molecular dimensions
have previously been used to manipulate molecular compositions in the gas
phase, but have so far been unable to offer controlled gas transport through
individual pores. Here, we show that gas flux through discrete angstrom-sized
pores in monolayer graphene can be detected and then controlled using
nanometer-sized gold clusters, which are formed on the surface of the graphene
and can migrate and partially block a pore. In samples without gold clusters,
we observe stochastic switching of the magnitude of the gas permeance, which we
attribute to molecular rearrangements of the pore. Our molecular valves could
be used, for example, to develop unique approaches to molecular synthesis that
are based on the controllable switching of a molecular gas flux, reminiscent of
ion channels in biological cell membranes and solid state nanopores.Comment: to appear in Nature Nanotechnolog
Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies
It has been assumed until very recently that all long-range correlations are
screened in three-dimensional melts of linear homopolymers on distances beyond
the correlation length characterizing the decay of the density
fluctuations. Summarizing simulation results obtained by means of a variant of
the bond-fluctuation model with finite monomer excluded volume interactions and
topology violating local and global Monte Carlo moves, we show that due to an
interplay of the chain connectivity and the incompressibility constraint, both
static and dynamical correlations arise on distances . These
correlations are scale-free and, surprisingly, do not depend explicitly on the
compressibility of the solution. Both monodisperse and (essentially)
Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure
Transcriptome Analysis and SNP Development Can Resolve Population Differentiation of Streblospio benedicti, a Developmentally Dimorphic Marine Annelid
Next-generation sequencing technology is now frequently being used to develop genomic tools for non-model organisms, which are generally important for advancing studies of evolutionary ecology. One such species, the marine annelid Streblospio benedicti, is an ideal system to study the evolutionary consequences of larval life history mode because the species displays a rare offspring dimorphism termed poecilogony, where females can produce either many small offspring or a few large ones. To further develop S. benedicti as a model system for studies of life history evolution, we apply 454 sequencing to characterize the transcriptome for embryos, larvae, and juveniles of this species, for which no genomic resources are currently available. Here we performed a de novo alignment of 336,715 reads generated by a quarter GS-FLX (Roche 454) run, which produced 7,222 contigs. We developed a novel approach for evaluating the site frequency spectrum across the transcriptome to identify potential signatures of selection. We also developed 84 novel single nucleotide polymorphism (SNP) markers for this species that are used to distinguish coastal populations of S. benedicti. We validated the SNPs by genotyping individuals of different developmental modes using the BeadXPress Golden Gate assay (Illumina). This allowed us to evaluate markers that may be associated with life-history mode
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