69 research outputs found
Surface plasmon polariton propagation around bends at a metal-dielectric interface
We analyze theoretically the propagation of surface plasmon polaritons about
a metallic corner with a finite bend radius, using a one-dimensional model
analogous to the scattering from a finite-depth potential well. We obtain
expressions for the energy reflection and transmission coefficients in the
short wavelength limit, as well as an upper bound for the transmittance. In
certain cases we find that propagation on non-planar interfaces may result in
lower losses than on flat surfaces, contrary to expectation. In addition, we
also find that the maximum transmittance depends non-monotonously on the bend
radius, allowing increased transmission with decreasing radius.Comment: For higher-quality figures, see
http://darkwing.uoregon.edu/~noeckel/papers.php#xref2
Tunable asymmetric reflectance in silver films near the percolation threshold
We report on the optical characterization of semicontinuous nanostructured
silver films exhibiting tunable optical reflectance asymmetries. The films are
obtained using a multi-step process, where a nanocrystalline silver film is
first chemically deposited on a glass substrate and then subsequently coated
with additional silver via thermal vacuum-deposition. The resulting films
exhibit reflectance asymmetries whose dispersions may be tuned both in sign and
in magnitude, as well as a universal, tunable spectral crossover point. We
obtain a correlation between the optical response and charge transport in these
films, with the spectral crossover point indicating the onset of charge
percolation. Such broadband, dispersion-tunable asymmetric reflectors may find
uses in future light-harvesting systems.Comment: 18 pages, 5 figures, accepted by Journal of Applied Physic
Curvature-induced radiation of surface plasmon polaritons propagating around bends
We present a theoretical study of the curvature-induced radiation of surface
plasmon polaritons (SPPs) propagating around bends at metal-dielectric
interfaces. We explain qualitatively how the curvature leads to distortion of
the phase front, causing the fields to radiate energy away from the
metal-dielectric interface. We then quantify, both analytically and
numerically, radiation losses and energy transmission efficiencies of SPPs
propagating around bends with varying radii- as well as sign-of-curvature.Comment: 9 pages, 8 figures, submitted to Physical Review
Enhanced surface plasmon resonance absorption in metal-dielectric-metal layered microspheres
We present a theoretical study of the dispersion relation of surface plasmon
resonances of mesoscopic metal-dielectric-metal microspheres. By analyzing the
solutions to Maxwell's equations, we obtain a simple geometric condition for
which the system exhibits a band of surface plasmon modes whose resonant
frequencies are weakly dependent on the multipole number. Using a modified Mie
calculation, we find that a large number of modes belonging to this
flat-dispersion band can be excited simultaneously by a plane wave, thus
enhancing the absorption cross-section. We demonstrate that the enhanced
absorption peak of the sphere is geometrically tunable over the entire visible
range.Comment: 4 pages, 3 figures, Accepted for publication, Optics Letters.
Revisions upon final revie
Asymmetric Reflectance and Cluster Size Effects in Silver Percolation Films
We develop a quantitative description of giant asymmetry in reflectance,
recently observed in semicontinuous metal films. The developed scaling-theory
based technique reproduces the spectral properties of semicontinuous
composites, as well as provides insight into the origin of experimentally
observed loss, reflectance, and transmittance anomalies in the vicinity of the
percolation threshold.Comment: 6 pages, 5 figure
Recognition Profile of Emotions in Natural and Virtual Faces
BACKGROUND: Computer-generated virtual faces become increasingly realistic including the simulation of emotional expressions. These faces can be used as well-controlled, realistic and dynamic stimuli in emotion research. However, the validity of virtual facial expressions in comparison to natural emotion displays still needs to be shown for the different emotions and different age groups. METHODOLOGY/PRINCIPAL FINDINGS: Thirty-two healthy volunteers between the age of 20 and 60 rated pictures of natural human faces and faces of virtual characters (avatars) with respect to the expressed emotions: happiness, sadness, anger, fear, disgust, and neutral. Results indicate that virtual emotions were recognized comparable to natural ones. Recognition differences in virtual and natural faces depended on specific emotions: whereas disgust was difficult to convey with the current avatar technology, virtual sadness and fear achieved better recognition results than natural faces. Furthermore, emotion recognition rates decreased for virtual but not natural faces in participants over the age of 40. This specific age effect suggests that media exposure has an influence on emotion recognition. CONCLUSIONS/SIGNIFICANCE: Virtual and natural facial displays of emotion may be equally effective. Improved technology (e.g. better modelling of the naso-labial area) may lead to even better results as compared to trained actors. Due to the ease with which virtual human faces can be animated and manipulated, validated artificial emotional expressions will be of major relevance in future research and therapeutic applications
The Brain Tumor Segmentation (BraTS) Challenge 2023: Focus on Pediatrics (CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs)
Pediatric tumors of the central nervous system are the most common cause of
cancer-related death in children. The five-year survival rate for high-grade
gliomas in children is less than 20\%. Due to their rarity, the diagnosis of
these entities is often delayed, their treatment is mainly based on historic
treatment concepts, and clinical trials require multi-institutional
collaborations. The MICCAI Brain Tumor Segmentation (BraTS) Challenge is a
landmark community benchmark event with a successful history of 12 years of
resource creation for the segmentation and analysis of adult glioma. Here we
present the CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs 2023 challenge, which
represents the first BraTS challenge focused on pediatric brain tumors with
data acquired across multiple international consortia dedicated to pediatric
neuro-oncology and clinical trials. The BraTS-PEDs 2023 challenge focuses on
benchmarking the development of volumentric segmentation algorithms for
pediatric brain glioma through standardized quantitative performance evaluation
metrics utilized across the BraTS 2023 cluster of challenges. Models gaining
knowledge from the BraTS-PEDs multi-parametric structural MRI (mpMRI) training
data will be evaluated on separate validation and unseen test mpMRI dataof
high-grade pediatric glioma. The CBTN-CONNECT-DIPGR-ASNR-MICCAI BraTS-PEDs 2023
challenge brings together clinicians and AI/imaging scientists to lead to
faster development of automated segmentation techniques that could benefit
clinical trials, and ultimately the care of children with brain tumors
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