321 research outputs found
Single phase microreactor for the continuous, high-temperature synthesis of <4¿nm superparamagnetic iron oxide nanoparticles
The reproducibility of key nanomaterial features is essential in nanomedicine applications where small changes of physical characteristics often lead to a very different behavior. In this regard, continuous microreactors are often advocated as a means to achieve highly precise synthesis of nanomaterials. However, when the synthesis must take place at high temperatures the use of these devices becomes restricted in terms of materials and practical problems (e.g. plugging of microchannels). Here we present the continuous synthesis of ultrasmall superparamagnetic iron oxide nanoparticles (SPIONs) through a polyol-based process at high temperatures (>200 °C). The microfluidic reactor designed allows SPION production at residence times under 1 min, was able to work continuously for 8 h without channel blockage and reached high production yields by coupling microreactors using stacked plates. The effect of operating conditions was optimized to produce homogeneous particles with a narrow particle size distribution. In summary, the microreactor developed in this work enables easy-to scale up, reproducible continuous production of SPIONs
Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at z~0.1
We have obtained new optical imaging and spectroscopic observations of 78
galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218
(z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25
cluster galaxies plus an additional six galaxies in the foreground and
background, a much lower success rate than what was found (65%) for a sample of
52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined
these data with our previous observations of Abell 2029 and Abell 2295 (both at
z = 0.08), which yields a sample of 156 galaxies. We evaluate several
parameters as a function of cluster environment: Tully-Fisher residuals,
H-alpha equivalent width, and rotation curve asymmetry, shape and extent.
Although H-alpha is more easily detectable in galaxies that are located further
from the cluster cores, we fail to detect a correlation between H-alpha extent
and galaxy location in those where it is detected, again in contrast with what
is found in the clusters of lesser richness. We fail to detect any
statistically significant trends for the other parameters in this study. The
zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5
sigma) than that found in nearby clusters, but the scatter is essentially
unchanged.Comment: 27 pages including 5 figures; accepted for publication in the
Astronomical Journa
Pixelization and Dynamic Range in Radio Interferometry
This study investigates some of the consequences of representing the sky by a
rectangular grid of pixels on the dynamic range of images derived from radio
interferometric measurements. In particular, the effects of image pixelization
coupled to the CLEAN deconvolution representation of the sky as a set of
discrete delta functions can limit the dynamic range obtained when representing
bright emission not confined to pixels on the grid. Sky curvature effects on
non-coplanar arrays will limit the dynamic range even if strong sources are
centered on a pixel in a "fly's eye" representation when such pixel is not
located at the corresponding facet's tangent point. Uncertainties in the
response function of the individual antennas as well as in the calibration of
actual data due to ionospheric, atmospheric or other effects will limit the
dynamic range even when using grid-less subtraction (i.e. in the visibility
domain) of strong sources located within the field of view of the observation.
A technique to reduce these effects is described and examples from an
implementation in the Obit package are given. Application of this technique
leads to significantly superior results without a significant increase in the
computing time.Comment: 8 pages, 4 figures (one double, one triple), to appear in Astronomy
and Astrophysics (accepted: September 5, 2008
Ataxia and focal dystonia in Kallmann syndrome
A case of Kallmann syndrome (KS) associated with rare neurological manifestations is presented. Cerebellar ataxia probably caused by a small posterior fossa and a focal dystonia affecting the left lower limb expand the spectrum of neurological manifestations occurring in KS. Further studies are needed to better understand these manifestations
Spontaneous formation of Au-Pt alloyed nanoparticles using pure nano-counterparts as starters: a ligand and size dependent process
In this work we investigate the formation of PtAu monodisperse alloyed nanoparticles by ageing pure metallic Au and Pt small nanoparticles (sNPs), nanoparticle size <5 nm, under certain conditions. We demonstrate that those bimetallic entities can be obtained by controlling the size of the initial metallic sNPs separately prepared and by selecting their appropriate capping agents. The formation of this spontaneous phenomenon was studied using HR-STEM, EDS, ionic conductivity, UV-Vis spectroscopy and cyclic voltammetry. Depending on the type of capping agent used and the size of the initial Au sNPs, three different materials were obtained: (i) AuPt bimetallic sNPs showing a surface rich in Au atoms, (ii) segregated Au and Pt sNPs and (iii) a mixture of bimetallic nanoparticles as well as Pt sNPs and Au NPs. Surface segregation energies and the nature of the reaction environment are the driving forces to direct the distribution of atoms in the bimetallic sNPs. PtAu alloyed nanoparticles were obtained after 150 h of reaction at room temperature if a weak capping agent was used for the stabilization of the nanoparticles. It was also found that Au atoms diffuse towards Pt sNPs, producing a surface enriched in Au atoms. This study shows that even pure nanoparticles are prone to be modified by the surrounding nanoparticles to give rise to new nanomaterials if atomic diffusion is feasible
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