280 research outputs found
Structural relaxation of E' gamma centers in amorphous silica
We report experimental evidence of the existence of two variants of the E'
gamma centers induced in silica by gamma rays at room temperature. The two
variants are distinguishable by the fine features of their line shapes in
paramagnetic resonance spectra. These features suggest that the two E' gamma
differ for their topology. We find a thermally induced interconversion between
the centers with an activation energy of about 34 meV. Hints are also found for
the existence of a structural configuration of minimum energy and of a
metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Manipulation and Optical Detection of Colloidal Functional Plasmonic Nanostructures in Microfluidic Systems
The very strong optical resonances of plasmonic nanostructures can be harnessed for sensitive detection of chemical and biomolecular analytes in small volumes. Here we describe an approach towards optical biosensing in microfluidic systems using plasmonic structures (functionalized gold nanoparticles) in colloidal suspension. The plasmonic nanoparticles provide the optical signal, in the form of resonant light scattering or absorption, and the microfluidic environment provides means for selectively manipulating the nanoparticles through fluid dynamics and electric fields. In the first part we discuss recent literature on functionalized colloidal particles and the methods for handling them in microfluidic systems. Then we experimentally address aspects of nanoparticle functionalization, detection through plasmonic resonant light scattering under dark-field illumination and the electrokinetic behavior of the particles under the action of an alternating electric field
Proof of the thermodynamical stability of the E' center in SiO2
The E' center is a paradigmatic radiation-induced defect in SiO2 whose
peculiar EPR and hyperfine activity has been known since over 40 years. This
center has been traditionally identified with a distorted, positively-charged
oxygen vacancy V_O+. However, no direct proof of the stability of this defect
has ever been provided, so that its identification is still strongly
incomplete. Here we prove directly that distorted V_O+ is metastable and that
it satisfies the key requirements for its identification as E', such as thermal
and optical response, and activation-deactivation mechanisms.Comment: RevTeX 4 pages, 2 figure
The use of high aspect ratio photoresist (SU-8) for super-hydrophobic pattern prototyping
In this work we present a reliable technique for the production of large areas of high aspect-ratio patterns and describe their use as model super-hydrophobic systems. The high thickness and straight sidewalls possible with SU-8 were used to generate dense patterns of small pillars. These photoresist patterns could be used directly, without the need for micromoulding. A method is given allowing resist thickness to be varied over a wide range and a bottom antireflective layer was used to simplify patterning on reflective substrates. This patterning technique allows rapid testing of wetting theories, as pattern size and depth can be varied simply and samples can be produced in sufficient numbers for laboratory use. We show how the static contact angle of water varies with pattern height for one sample-pattern and how static and dynamic contact angles vary with dimension using high aspect-ratio patterns
Characterization of E'delta and triplet point defects in oxygen deficient amorphous silicon dioxide
We report an experimental study by electron paramagnetic resonance (EPR) of
gamma ray irradiation induced point defects in oxygen deficient amorphous SiO2
materials. We have found that three intrinsic (E'gamma, E'delta and triplet)
and one extrinsic ([AlO4]0) paramagnetic centers are induced. All the
paramagnetic defects but E'gamma center are found to reach a concentration
limit value for doses above 10^3 kGy, suggesting a generation process from
precursors. Isochronal thermal treatments of a sample irradiated at 10^3 kGy
have shown that for T>500 K the concentrations of E'gamma and E'delta centers
increase concomitantly to the decrease of [AlO4]0. This occurrence speaks for
an hole transfer process from [AlO4]0 centers to diamagnetic precursors of E'
centers proving the positive charge state of the thermally induced E'gamma and
E'delta centers and giving insight on the origin of E'gamma from an oxygen
vacancy. A comparative study of the E'delta center and of the 10 mT doublet EPR
signals on three distinct materials subjected to isochronal and isothermal
treatments, has shown a quite general linear correlation between these two EPR
signals. This result confirms the attribution of the 10 mT doublet to the
hyperfine structure of the E'delta center, originating from the interaction of
the unpaired electron with a nucleus of 29Si (I=1/2). Analogies between the
microwave saturation properties of E'gamma and E'delta centers and between
those of their hyperfine structures are found and suggest that the unpaired
electron wave function involves similar Si sp3 hybrid orbitals; specifically,
for the E'delta the unpaired electron is supposed to be delocalized over four
such orbitals of four equivalent Si atoms.Comment: Approved for publication in Physical Review
Conservation must capitalise on climate’s moment
The health of the natural environment has never been a greater concern, but attention to biodiversity loss is being eclipsed by the climate crisis. We argue that conservationists must seize the agenda to put biodiversity at the heart of climate policy
The electronic structure of amorphous silica: A numerical study
We present a computational study of the electronic properties of amorphous
SiO2. The ionic configurations used are the ones generated by an earlier
molecular dynamics simulations in which the system was cooled with different
cooling rates from the liquid state to a glass, thus giving access to
glass-like configurations with different degrees of disorder [Phys. Rev. B 54,
15808 (1996)]. The electronic structure is described by a tight-binding
Hamiltonian. We study the influence of the degree of disorder on the density of
states, the localization properties, the optical absorption, the nature of
defects within the mobility gap, and on the fluctuations of the Madelung
potential, where the disorder manifests itself most prominently. The
experimentally observed mismatch between a photoconductivity threshold of 9 eV
and the onset of the optical absorption around 7 eV is interpreted by the
picture of eigenstates localized by potential energy fluctuations in a mobility
gap of approximately 9 eV and a density of states that exhibits valence and
conduction band tails which are, even in the absence of defects, deeply located
within the former band gap.Comment: 21 pages of Latex, 5 eps figure
Osteosclerosis in the extinct Cayaoa Bruneti (Aves, anseriformes) : insights on behavior and fligftlessness
Fil: Mendoza, Ricardo de. DivisiĂłn PaleontologĂa Vertebrados. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Tambussi, Claudia Patricia. Centro de Investigaciones en Ciencias de la Tierra (CICTERRA). Universidad Nacional de CĂłrdoba; Argentin
Three-dimensional in vitro culture models in oncology research
Cancer is a multifactorial disease that is responsible for 10 million deaths per year. The intra- and inter-heterogeneity of malignant tumors make it difficult to develop single targeted approaches. Similarly, their diversity requires various models to investigate the mechanisms involved in cancer initiation, progression, drug resistance and recurrence. Of the in vitro cell-based models, monolayer adherent (also known as 2D culture) cell cultures have been used for the longest time. However, it appears that they are often less appropriate than the three-dimensional (3D) cell culture approach for mimicking the biological behavior of tumor cells, in particular the mechanisms leading to therapeutic escape and drug resistance. Multicellular tumor spheroids are widely used to study cancers in 3D, and can be generated by a multiplicity of techniques, such as liquid-based and scaffold-based 3D cultures, microfluidics and bioprinting. Organoids are more complex 3D models than multicellular tumor spheroids because they are generated from stem cells isolated from patients and are considered as powerful tools to reproduce the disease development in vitro. The present review provides an overview of the various 3D culture models that have been set up to study cancer development and drug response. The advantages of 3D models compared to 2D cell cultures, the limitations, and the fields of application of these models and their techniques of production are also discussed
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