67,956 research outputs found
Optimization of Nanoparticle-Based SERS Substrates through Large-Scale Realistic Simulations
Surface-enhanced Raman scattering (SERS) has
become a widely used spectroscopic technique for chemical
identification, providing unbeaten sensitivity down to the singlemolecule
level. The amplification of the optical near field
produced by collective electron excitations plasmons in
nanostructured metal surfaces gives rise to a dramatic increase
by many orders of magnitude in the Raman scattering intensities
from neighboring molecules. This effect strongly depends on
the detailed geometry and composition of the plasmonsupporting
metallic structures. However, the search for
optimized SERS substrates has largely relied on empirical
data, due in part to the complexity of the structures, whose
simulation becomes prohibitively demanding. In this work, we
use state-of-the-art electromagnetic computation techniques to
produce predictive simulations for a wide range of nanoparticle-based SERS substrates, including realistic configurations
consisting of random arrangements of hundreds of nanoparticles with various morphologies. This allows us to derive rules of
thumb for the influence of particle anisotropy and substrate coverage on the obtained SERS enhancement and optimum spectral
ranges of operation. Our results provide a solid background to understand and design optimized SERS substrates.Peer ReviewedPostprint (published version
Real-time Model-based Image Color Correction for Underwater Robots
Recently, a new underwater imaging formation model presented that the
coefficients related to the direct and backscatter transmission signals are
dependent on the type of water, camera specifications, water depth, and imaging
range. This paper proposes an underwater color correction method that
integrates this new model on an underwater robot, using information from a
pressure depth sensor for water depth and a visual odometry system for
estimating scene distance. Experiments were performed with and without a color
chart over coral reefs and a shipwreck in the Caribbean. We demonstrate the
performance of our proposed method by comparing it with other statistic-,
physic-, and learning-based color correction methods. Applications for our
proposed method include improved 3D reconstruction and more robust underwater
robot navigation.Comment: Accepted at the 2019 IEEE/RSJ International Conference on Intelligent
Robots and Systems (IROS
Angiogenesis in tissue engineering : Breathing life into constructed tissue substitutes
Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ
Proton pygmy resonances: predictions for N=20 isotones
We study theoretically the low-energy electric-dipole response of N=20
isotones. We present results from a quasiparticle random-phase approximation
(QRPA) and a continuum random-phase approximation (CRPA), and we compare them
with results for the mirror Z=20 nuclei. According to our analysis, enhanced E1
strength is expected energetically well below the giant dipole resonance in the
proton-rich isotones. Large amounts of E1 strength in the asymmetric N=20
isotones are predicted, unlike their equally asymmetric Z=20 mirror nuclei,
pointing unambiguously to the role of structural effects such as loose binding.
A proton-skin oscillation could develop especially in 46Fe. The proper
description of non localized threshold transitions and the nucleon effective
mass in mean-field treatments may affect theoretical predictions. We call for
systematic theoretical investigations to quantify the role bulk-matter
properties, in anticipation of measurements of E1 transitions in proton-rich
nuclei.Comment: 10 pages, incl. 9 figures and 2 tables; v2: some rephrasing and
clarifications, corrected Fig.
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