3,800 research outputs found
Mercury removal in wastewater by iron oxide nanoparticles
Mercury is one of the persistent pollutants in wastewater; it is becoming a severe environmental and public health problem, this is why nowadays its removal is an obligation. Iron oxide nanoparticles are receiving much attention due to their properties, such as: great biocompatibility, ease of separation, high relation of surface-area to volume, surface modifiability, reusability, excellent magnetic properties and relative low cost. In this experiment, Fe3O4 and Îł-Fe2O3 nanoparticles were synthesized using iron salts and NaOH as precipitation agents, and Aloe Vera as stabilizing agent; then these nanoparticles were characterized by three different measurements: first, using a Zetasizer Nano ZS for their size estimation, secondly UV-visible spectroscopy which showed the existence of resonance of plasmon at λmaxâŒ360 nm, and lastly by Scanning Electron Microscopy (SEM) to determine nanoparticles form. The results of this characterization showed that the obtained Iron oxides nanoparticles have a narrow size distribution (âŒ100nm). Mercury removal of 70% approximately was confirmed by atomic absorption spectroscopy measurements
Nonlinear viscosity and velocity distribution function in a simple longitudinal flow
A compressible flow characterized by a velocity field is
analyzed by means of the Boltzmann equation and the Bhatnagar-Gross-Krook
kinetic model. The sign of the control parameter (the longitudinal deformation
rate ) distinguishes between an expansion () and a condensation ()
phenomenon. The temperature is a decreasing function of time in the former
case, while it is an increasing function in the latter. The non-Newtonian
behavior of the gas is described by a dimensionless nonlinear viscosity
, that depends on the dimensionless longitudinal rate . The
Chapman-Enskog expansion of in powers of is seen to be only
asymptotic (except in the case of Maxwell molecules). The velocity distribution
function is also studied. At any value of , it exhibits an algebraic
high-velocity tail that is responsible for the divergence of velocity moments.
For sufficiently negative , moments of degree four and higher may diverge,
while for positive the divergence occurs in moments of degree equal to or
larger than eight.Comment: 18 pages (Revtex), including 5 figures (eps). Analysis of the heat
flux plus other minor changes added. Revised version accepted for publication
in PR
Depth profile of the ferromagnetic order in a YBaCuO / LaCaMnO superlattice on a LSAT substrate: a polarized neutron reflectometry study
Using polarized neutron reflectometry (PNR) we have investigated a
YBa2Cu3O7(10nm)/La2/3Ca1/3MnO3(9nm)]10 (YBCO/LCMO) superlattice grown by pulsed
laser deposition on a La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrate. Due to the
high structural quality of the superlattice and the substrate, the specular
reflectivity signal extends with a high signal-to-background ratio beyond the
fourth order superlattice Bragg peak. This allows us to obtain more detailed
and reliable information about the magnetic depth profile than in previous PNR
studies on similar superlattices that were partially impeded by problems
related to the low temperature structural transitions of the SrTiO3 substrates.
In agreement with the previous reports, our PNR data reveal a strong magnetic
proximity effect showing that the depth profile of the magnetic potential
differs significantly from the one of the nuclear potential that is given by
the YBCO and LCMO layer thickness. We present fits of the PNR data using
different simple block-like models for which either a ferromagnetic moment is
induced on the YBCO side of the interfaces or the ferromagnetic order is
suppressed on the LCMO side. We show that a good agreement with the PNR data
and with the average magnetization as obtained from dc magnetization data can
only be obtained with the latter model where a so-called depleted layer with a
strongly suppressed ferromagnetic moment develops on the LCMO side of the
interfaces. The models with an induced ferromagnetic moment on the YBCO side
fail to reproduce the details of the higher order superlattice Bragg peaks and
yield a wrong magnitude of the average magnetization. We also show that the PNR
data are still consistent with the small, ferromagnetic Cu moment of 0.25muB
that was previously identified with x-ray magnetic circular dichroism and x-ray
resonant magnetic reflectometry measurements on the same superlattice.Comment: 11 pages, 7 figure
Pulsed laser deposition growth of heteroepitaxial YBa2Cu3O7/La0.67Ca0.33MnO3 superlattices on NdGaO3 and Sr0.7La0.3Al0.65Ta0.35O3 substrates
Heteroepitaxial superlattices of [YBa2Cu3O7(n)/ La0.67Ca0.33MnO3(m)]x, where
n and m are the number of YBCO and LCMO monolayers and x the number of bilayer
repetitions, have been grown with pulsed laser deposition on NdGaO3 (110) and
Sr0.7La0.3Al0.65Ta0.35O3 (LSAT) (001). These substrates are well lattice
matched with YBCO and LCMO and, unlike the commonly used SrTiO3, they do not
give rise to complex and uncontrolled strain effects due to structural
transitions at low temperature. The growth dynamics and the structure have been
studied in-situ with reflection high energy electron diffraction (RHEED) and
ex-situ with scanning transmission electron microscopy (STEM), x-ray
diffraction, and neutron reflectometry. The individual layers are found to be
flat and continuous over long lateral distances with sharp and coherent
interfaces and with a well-defined thickness of the individual layer. The only
visible defects are antiphase boundaries in the YBCO layers that originate from
perovskite unit cell height steps at the interfaces with the LCMO layers. We
also find that the first YBCO monolayer at the interface with LCMO has an
unusual growth dynamics and is lacking the CuO chain layer while the subsequent
YBCO layers have the regular Y-123 structure. Accordingly, the CuO2 bilayers at
both the LCMO/YBCO and the YBCO/LCMO interfaces are lacking one of their
neighboring CuO chain layers and thus half of their hole doping reservoir.
Nevertheless, from electric transport measurements on asuperlattice with n=2 we
obtain evidence that the interfacial CuO2 bilayers remain conducting and even
exhibit the onset of a superconducting transition at very low temperature.
Finally, we show from dc magnetization and neutron reflectometry measurements
that the LCMO layers are strongly ferromagnetic
Remarks on the naturality of quantization
Hamiltonian quantization of an integral compact symplectic manifold M depends
on a choice of compatible almost complex structure J. For open sets U in the
set of compatible almost complex structures and small enough values of Planck's
constant, the Hilbert spaces of the quantization form a bundle over U with a
natural connection. In this paper we examine the dependence of the Hilbert
spaces on the choice of J, by computing the semi-classical limit of the
curvature of this connection. We also show that parallel transport provides a
link between the action of the group Symp(M) of symplectomorphisms of M and the
Schrodinger equation.Comment: 20 page
Strengthening the Cohomological Crepant Resolution Conjecture for Hilbert-Chow morphisms
Given any smooth toric surface S, we prove a SYM-HILB correspondence which
relates the 3-point, degree zero, extended Gromov-Witten invariants of the
n-fold symmetric product stack [Sym^n(S)] of S to the 3-point extremal
Gromov-Witten invariants of the Hilbert scheme Hilb^n(S) of n points on S. As
we do not specialize the values of the quantum parameters involved, this result
proves a strengthening of Ruan's Cohomological Crepant Resolution Conjecture
for the Hilbert-Chow morphism from Hilb^n(S) to Sym^n(S) and yields a method of
reconstructing the cup product for Hilb^n(S) from the orbifold invariants of
[Sym^n(S)].Comment: Revised versio
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