1,757 research outputs found
Printable Nanoscopic Metamaterial Absorbers and Images with Diffraction-Limited Resolution
The fabrication of functional metamaterials with extreme feature resolution
finds a host of applications such as the broad area of surface/light
interaction. Non-planar features of such structures can significantly enhance
their performance and tunability, but their facile generation remains a
challenge. Here, we show that carefully designed out-of-plane nanopillars made
of metal-dielectric composites integrated in a metal-dielectric-nanocomposite
configuration, can absorb broadband light very effectively. We further
demonstrate that electrohydrodynamic printing in a rapid nanodripping mode, is
able to generate precise out-of-plane forests of such composite nanopillars
with deposition resolutions at the diffraction limit on flat and non-flat
substrates. The nanocomposite nature of the printed material allows the
fine-tuning of the overall visible light absorption from complete absorption to
complete reflection by simply tuning the pillar height. Almost perfect
absorption (~95%) over the entire visible spectrum is achieved by a nanopillar
forest covering only 6% of the printed area. Adjusting the height of individual
pillar groups by design, we demonstrate on-demand control of the gray scale of
a micrograph with a spatial resolution of 400 nm. These results constitute a
significant step forward in ultra-high resolution facile fabrication of
out-of-plane nanostructures, important to a broad palette of light design
applications. nanostructures, important to a broad palette of light design
applications
Topographic hub maps of the human structural neocortical network
Hubs within the neocortical structural network determined by graph theoretical analysis play a crucial role in brain function. We mapped neocortical hubs topographically, using a sample population of 63 young adults. Subjects were imaged with high resolution structural and diffusion weighted magnetic resonance imaging techniques. Multiple network configurations were then constructed per subject, using random parcellations to define the nodes and using fibre tractography to determine the connectivity between the nodes. The networks were analysed with graph theoretical measures. Our results give reference maps of hub distribution measured with betweenness centrality and node degree. The loci of the hubs correspond with key areas from known overlapping cognitive networks. Several hubs were asymmetrically organized across hemispheres. Furthermore, females have hubs with higher betweenness centrality and males have hubs with higher node degree. Female networks have higher small-world indices
ECO and RESOLVE: Galaxy Disk Growth in Environmental Context
We study the relationships between galaxy environments and galaxy properties
related to disk (re)growth, considering two highly complete samples that are
approximately baryonic mass limited into the high-mass dwarf galaxy regime, the
Environmental COntext (ECO) catalog (data release herein) and the B-semester
region of the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. We
quantify galaxy environments using both group identification and smoothed
galaxy density field methods. We use by-eye and quantitative morphological
classifications plus atomic gas content measurements and estimates. We find
that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright
disk host galaxies all become distinctly more common below group halo mass
~10^11.5 Msun, implying that this low group halo mass regime may be a preferred
regime for significant disk growth activity. We also find that blue early-type
and blue late-type galaxies inhabit environments of similar group halo mass at
fixed baryonic mass, consistent with a scenario in which blue early types can
regrow late-type disks. In fact, we find that the only significant difference
in the typical group halo mass inhabited by different galaxy classes is for
satellite galaxies with different colors, where at fixed baryonic mass red
early and late types have higher typical group halo masses than blue early and
late types. More generally, we argue that the traditional
morphology-environment relation (i.e., that denser environments tend to have
more early types) can be largely attributed to the morphology-galaxy mass
relation for centrals and the color-environment relation for satellites.Comment: 26 pages and 28 figures; v2 contains minor figure and text updates to
match final published version in ApJ; ECO data table release now available at
http://resolve.astro.unc.edu/pages/data.ph
Genetic diversity in Treponema pallidum: Implications for pathogenesis, evolution and molecular diagnostics of syphilis and yaws
AbstractPathogenic uncultivable treponemes, similar to syphilis-causing Treponema pallidum subspecies pallidum, include T. pallidum ssp. pertenue, T. pallidum ssp. endemicum and Treponema carateum, which cause yaws, bejel and pinta, respectively. Genetic analyses of these pathogens revealed striking similarity among these bacteria and also a high degree of similarity to the rabbit pathogen, Treponema paraluiscuniculi, a treponeme not infectious to humans. Genome comparisons between pallidum and non-pallidum treponemes revealed genes with potential involvement in human infectivity, whereas comparisons between pallidum and pertenue treponemes identified genes possibly involved in the high invasivity of syphilis treponemes. Genetic variability within syphilis strains is considered as the basis of syphilis molecular epidemiology with potential to detect more virulent strains, whereas genetic variability within a single strain is related to its ability to elude the immune system of the host. Genome analyses also shed light on treponemal evolution and on chromosomal targets for molecular diagnostics of treponemal infections
Fully broadband vAPP coronagraphs enabling polarimetric high contrast imaging
We present designs for fully achromatic vector Apodizing Phase Plate (vAPP)
coronagraphs, that implement low polarization leakage solutions and achromatic
beam-splitting, enabling observations in broadband filters. The vAPP is a pupil
plane optic, inducing the phase through the inherently achromatic geometric
phase. We discuss various implementations of the broadband vAPP and set
requirements on all the components of the broadband vAPP coronagraph to ensure
that the leakage terms do not limit a raw contrast of 1E-5. Furthermore, we
discuss superachromatic QWPs based of liquid crystals or quartz/MgF2
combinations, and several polarizer choices. As the implementation of the
(broadband) vAPP coronagraph is fully based on polarization techniques, it can
easily be extended to furnish polarimetry by adding another QWP before the
coronagraph optic, which further enhances the contrast between the star and a
polarized companion in reflected light. We outline several polarimetric vAPP
system designs that could be easily implemented in existing instruments, e.g.
SPHERE and SCExAO.Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and
Instrumentation 201
Ultrafast optical switching of three-dimensional Si inverse opal photonic band gap crystals
We present ultrafast optical switching experiments on 3D photonic band gap
crystals. Switching the Si inverse opal is achieved by optically exciting free
carriers by a two-photon process. We probe reflectivity in the frequency range
of second order Bragg diffraction where the photonic band gap is predicted. We
find good experimental switching conditions for free-carrier plasma frequencies
between 0.3 and 0.7 times the optical frequency: we thus observe a large
frequency shift of up to D omega/omega= 1.5% of all spectral features including
the peak that corresponds to the photonic band gap. We deduce a corresponding
large refractive index change of Dn'_Si/n'_Si= 2.0% and an induced absorption
length that is longer than the sample thickness. We observe a fast decay time
of 21 ps, which implies that switching could potentially be repeated at GHz
rates. Such a high switching rate is relevant to future switching and
modulation applications
Exploring the Anatomical Basis of Effective Connectivity Models with DTI-Based Fiber Tractography
Diffusion tensor imaging (DTI) is considered to be a promising tool for revealing the anatomical basis of functional networks. In this study, we investigate the potential of DTI to provide the anatomical basis of paths that are used in studies of effective connectivity, using structural equation modeling. We have taken regions of interest from eight previously published studies, and examined the connectivity as defined by DTI-based fiber tractography between these regions. The resulting fiber tracts were then compared with the paths proposed in the original studies. For a substantial number of connections, we found fiber tracts that corresponded to the proposed paths. More importantly, we have also identified a number of cases in which tractography suggested direct connections which were not included in the original analyses. We therefore conclude that DTI-based fiber tractography can be a valuable tool to study the anatomical basis of functional networks
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