323 research outputs found
Poly(acrylic acid)-coated iron oxide nanoparticles : quantitative evaluation of the coating properties and applications for the removal of a pollutant dye
In this work, 6 to 12 nm iron oxide nanoparticles were synthesized and coated
with poly(acrylic acid) chains of molecular weight 2100 g/mol. Based on a
quantitative evaluation of the dispersions, the bare and coated particles were
thoroughly characterized. The number densities of polymers adsorbed at the
particle surface and of available chargeable groups were found to be 1.9 +/-
0.3 nm-2 and 26 +/- 4 nm-2, respectively. Occurring via a multi-site binding
mechanism, the electrostatic coupling leads to a solid and resilient anchoring
of the chains. To assess the efficacy of the particles for pollutant
remediation, the adsorption isotherm of methylene blue molecules, a model of
pollutant, was determined. The excellent agreement between the predicted and
measured amounts of adsorbed dyes suggests that most carboxylates participate
to the complexation and adsorption mechanisms. An adsorption of 830 mg/g was
obtained. This quantity compares well with the highest values available for
this dye.Comment: 14 pages 5 figures, accepted 06-Dec-2012; Journal of Colloid and
Interface Science (2013
Structure factors of harmonic and anharmonic Fibonacci chains by molecular dynamics simulations
The dynamics of quasicrystals is characterized by the existence of phason
excitations in addition to the usual phonon modes. In order to investigate
their interplay on an elementary level we resort to various one-dimensional
model systems. The main observables are the static, the incoherent, and the
coherent structure factor, which are extracted from molecular dynamics
simulations. For the validation of the algorithms, results for the harmonic
periodic chain are presented. We then study the Fibonacci chain with harmonic
and anharmonic interaction potentials. In the dynamic Fibonacci chain
neighboring atoms interact by double-well potentials allowing for phason flips.
The difference between the structure factors of the dynamic and the harmonic
Fibonacci chain lies in the temperature dependence of the phonon line width. If
a bias is introduced in the well depth, dispersionless optic phonon bands split
off.Comment: 12 pages, 15 figure
Influence of the Environment Fluctuations on Incoherent Neutron Scattering Functions
In extending the conventional dynamic models, we consider a simple model to
account for the environment fluctuations of particle atoms in a protein system
and derive the elastic incoherent structure factor (EISF) and the incoherent
scattering correlation function C(Q,t) for both the jump dynamics between sites
with fluctuating site interspacing and for the diffusion inside a fluctuating
sphere. We find that the EISF of the system (or the normalized elastic
intensity) is equal to that in the absence of fluctuations averaged over the
distribution of site interspacing or sphere radius a. The scattering
correlation function is ,
where the average is taken over the Q-dependent effective distribution of
relaxation rates \lambda_n(a) and \psi(t) is the correlation function of the
length a. When \psi(t)=1, the relaxation of C(Q,t) is exponential for the jump
dynamics between sites (since \lambda_n(a) is independent of a) while it is
nonexponential for diffusion inside a sphere.Comment: 7 pages, 7 eps figure
The dynamical properties of the aromatic hydrogen bond in NH4 C6H5 4 B from quasielastic neutron scattering
A IMPORTÂNCIA DA RECREAÇÃO PARA O ENSINO DO ATLETISMO NA ESCOLA: UM RELATO DE EXPERIÊNCIA
A Educação Física é de suma importância para o desenvolvimento dos alunos, abrangendo as dimensões conceitual, dimensional procedimental e atitudinal, preparando assim, o aluno para a sociedade. O objetivo deste trabalho é relatar os acontecimentos do Estágio Curricular Multidisciplinar I, que foi realizado em uma escola municipal do interior do município de Alpestre-RS. No estágio foi realizado atividades de atletismo que proporcionaram aos alunos um desenvolvimento integral, por meio de vivências que exploraram as habilidades motoras básicas como correr, saltar, pular, arremessar de forma simples e prazerosa, respeitando a individualidade de cada um e estimulando o desenvolvimento motor, cognitivo, afetivo e social. A recreação é importantíssima na fase escolar das crianças, pois desenvolve a integração com o grupo, a locomoção, o raciocínio, a psicomotricidade, o espírito esportivo, a resistência física e a psicológica, a criação de estratégias, a motivação, a criatividade, a comunicação, o espírito de liderança, as noções de tempo e espaço, entre outros. Os métodos utilizados nas aulas foram prioritariamente os métodos parcial, recreativo e global. O Estágio proporcionou a vivencia da docência, estar efetivamente de frente a uma turma, aplicando nas aulas os conhecimentos aprendidos na universidade, vivenciando a função do professor e as dificuldades que são encontradas no decorrer do ano letivo
Molecular dynamics of glycerol and glycerol-trehalose bioprotectant solutions nanoconfined in porous silicon
Glycerol and trehalose-glycerol binary solutions are glass-forming liquids
with remarkable bioprotectant properties. Incoherent quasielastic neutron
scattering (QENS) is used to reveal the different effects of nanoconfinement
and addition of trehalose on the molecular dynamics in the normal liquid and
supercooled liquid phases, on a nanosecond timescale. Confinement has been
realized in straight channels of diameter D=8 nm formed by porous silicon. It
leads to a faster and more inhomogeneous relaxation dynamics deep in the liquid
phase. This confinement effect remains at lower temperature where it affects
the glassy dynamics. The glass transitions of the confined systems are shifted
to low temperature with respect to the bulk ones. Adding trehalose tends to
slow down the overall glassy dynamics and increases the non-exponential
character of the structural relaxation. Unprecedented results are obtained for
the binary bioprotectant solution, which exhibits an extremely non-Debye
relaxation dynamics as a result of the combination of the effects of
confinement and mixing of two constituents
SPHERES, J\"ulich's High-Flux Neutron Backscattering Spectrometer at FRM II
SPHERES (SPectrometer with High Energy RESolution) is a third-generation
neutron backscattering spectrometer, located at the 20 MW German neutron source
FRM II and operated by the Juelich Centre for Neutron Science. It offers an
energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31
micro-eV, and a signal-to-noise ratio of up to 1750:1.Comment: 12 pages, 7 figures, 2 tables. Supplemental material consists of 3
pages, 2 figures, 2 table
Molecular dynamics of a short range ordered smectic phase nanoconfined into porous silicon
4-n-octyl-4-cyanobiphenyl (8CB) has been recently shown to display an unusual
sequence of phases when confined into porous silicon (PSi). The gradual
increase of oriented short-range smectic (SRS) correlations in place of a phase
transition has been interpreted as a consequence of the anisotropic quenched
disorder induced by confinement in PSi. Combining two quasielastic neutron
scattering experiments with complementary energy resolutions, we present the
first investigation of the individual molecular dynamics of this system. A
large reduction of the molecular dynamics is observed in the confined liquid
phase, as a direct consequence of the dynamical boundary conditions imposed by
the confinement. Temperature fixed window scans (FWS) reveal a continuous
'glass-like' reduction of the molecular dynamics of the confined liquid and SRS
phases on cooling down to 250 K, where a solid-like behavior is finally reached
by a two steps crystallization process
Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase
The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 Å, c ≈ 6.7 Å) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions
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