5 research outputs found
SPH fluids for viscous jet buckling
We present a novel meshfree technique for animating\ud
free surface viscous liquids with jet buckling effects, such as\ud
coiling and folding. Our technique is based on Smoothed Particle\ud
Hydrodynamics (SPH) fluids and allows more realistic and\ud
complex viscous behaviors than the preceding SPH frameworks\ud
in computer animation literature. The viscous liquid is modeled\ud
by a non-Newtonian fluid flow and the variable viscosity under\ud
shear stress is achieved using a viscosity model known as Cross\ud
model. The proposed technique is efficient and stable, and our\ud
framework can animate scenarios with high resolution of SPH\ud
particles in which the simulation speed is significantly accelerated\ud
by using Computer Unified Device Architecture (CUDA)\ud
computing platform. This work also includes several examples\ud
that demonstrate the ability of our technique.FAPESP - processos nos. 2013/19760-5 e 2014/11981-5FAPES - processos no. 53600100/11CNP
Superparamagnetic Microspheres with Controlled Macroporosity Generated in Microfluidic Devices
A microfluidic approach to preparing superparamagnetic
microspheres with tunable porosity is described. In this method, droplets
consisting of iron oxide nanoparticles, a functional polymer and solvent
are formed in a microfluidic channel. The droplets are subsequently
collected in solutions of sodium dodecyl sulfate (SDS) where the solvent
is left to diffuse out of the droplet phase. By adjusting the concentration
of the SDS and the polarity of the solvent of the dispersed phase,
the porosity of the microparticles is controlled from non porous to
porous structure. The formation of the pores is shown to depend on
the rate at which solvent diffuses out of the droplet phase and the
availability of SDS to adsorb at the droplet interface
Manipulation and Quantification of Graphene Oxide Flake Size: Photoluminescence and Cytotoxicity
Single-layered
graphene oxide (GO) has exhibited great promise in the areas of sensing,
membrane filtration, supercapacitors, bioimaging, and therapeutic
carriers because of its biocompatibility, large surface area, and
electrochemical, photoluminescent, and optical properties. To elucidate
how the physical dimensions of GO affect its intrinsic properties,
we employed sonication to produce more than 130 different sizes of
GO in aqueous dispersion and implemented new approaches to characterize
various GO properties as a function of the average flake size. New
protocols were developed to determine and compare the flake size of
GO dispersions sonicated with energies up to 20 MJ/g by using dynamic
light scattering and atomic force microscopy (AFM). The relationship
between the average flake size and sonication energy per unit mass
of GO was observed to follow a power law. AFM height measurements
showed that the sonication of GO yielded monolayered flakes. Photoluminescence
of GO was characterized as a function of the sonication energy (or
the average flake size which is the monotonic function of the sonication
energy), excitation wavelength, and pH of the dispersion. The strong
dependence of the photoluminescence intensity on pH control and the
variation of the photoluminescence intensity with different flake
sizes were observed. An intense photoluminescence signal, likely related
to the separation of the oxidative debris from the GO framework, was
found at the highest sonication energies (<i>E</i> ≳
15 MJ/g) or under extremely alkaline conditions (pH ≳ 11).
The cytotoxicity of GO was studied with various flake sizes. Size-
and concentration-dependent cytotoxicity was observed for cell lines
NIH 3T3 and A549. The NIH 3T3 cell line also demonstrated time-dependent
cytotoxicity
Ensemble and Single Particle Fluorescence Characterization of Dye-Labeled Cellulose Nanocrystals
Cellulose
nanocrystals
(CNCs) have been covalently labeled with
both fluorescein and rhodamine and studied by a combination of UV–vis
absorption spectroscopy and ensemble and single molecule fluorescence
spectroscopy. For all samples, the fluorescence anisotropy and lifetimes
were consistent with effects expected for covalently bound dye molecules.
Low dye loading levels (∼0.1 dye/particle) were estimated for
the fluorescein-labeled CNC which coupled with the strong pH dependence
make this a less suitable fluorophore for most applications. Rhodamine-labeled
CNCs were prepared from both sulfated and carboxylated CNCs and had
loading levels that varied from 0.25 to ∼15 dye molecules/CNC.
For the sulfated samples, the absorption due to (nonfluorescent) dimeric
dye increased with dye loading; in contrast, the carboxylated sample,
which had the highest rhodamine content, had a low dimer yield. Single
particle fluorescence studies for two of the rhodamine-labeled CNCs
demonstrated that individual particles are readily detected by their
stepwise blinking/bleaching behavior and by polarization effects.
Overall, the results indicate the importance of understanding the
effects of loading on dye photophysics to select an optimal dye concentration
to maximize sensitivity while minimizing the effect of the dye on
the CNC behavior. The results also demonstrate that CNCs with relatively
low dye loadings (e.g., ∼1 dye/particle) are readily detectable
by fluorescence and should be adequate for use in fluorescence-based
biological assays or to probe the distribution of CNCs in composite
materials
Changes in Order Parameters Associated with Ceramide-Mediated Membrane Reorganization Measured Using pTIRFM
The enzymatic generation of ceramide
has significant effects on
the biophysical properties of lipid bilayers and can lead to the extensive
reorganization of cell membranes. We have synthesized and characterized
a headgroup-labeled fluorescent lipid probe (NBD-ceramide, NBD-Cer)
and demonstrated that it can be used for polarized total internal
reflection fluorescence microscopy experiments to probe changes in
membrane order that result from ceramide incorporation. NBD-Cer measures
significantly higher order parameters for the liquid-ordered (L<sub>o</sub>) domains (⟨<i>P</i><sub>2</sub>⟩
= 0.40 ± 0.03) than for the liquid-disordered phase (L<sub>d</sub>, fluid, ⟨<i>P</i><sub>2</sub>⟩ = 0.22 ±
0.02) of phase-separated bilayers prepared from egg sphingomyelin,
dioleolyphosphatidylcholine, and cholesterol mixtures. The probe also
responds to changes in packing induced by the direct incorporation
of ceramide or the variation in the ionic strength of the aqueous
medium. Order parameter maps obtained after enzyme treatment of bilayers
with coexisting L<sub>o</sub> and L<sub>d</sub> phases show two distinct
types of behavior. In regions of high enzyme activity, the initial
L<sub>o</sub>/L<sub>d</sub> domains are replaced by large, dark features
that have high membrane order corroborating previous hypotheses that
these are ceramide-enriched regions of the membrane. In areas of low
enzyme activity, the size and shape of the L<sub>o</sub> domains are
conserved, but there is an increase in the order parameter for the
initial L<sub>d</sub> phase (⟨<i>P</i><sub>2</sub>⟩ = 0.30 ± 0.01). This is attributed to the incorporation
of ceramide in the L<sub>o</sub> domains with the concomitant expulsion
of cholesterol into the surrounding fluid phase, increasing its order
parameter