149 research outputs found
Inducing and Optimizing Magnetism in Graphene Nanomesh
Using first-principles calculations, we explore the electronic and magnetic
properties of graphene nanomesh (GNM), a regular network of large vacancies,
produced either by lithography or nanoimprint. When removing an equal number of
A and B sites of the graphene bipartite lattice, the nanomesh made mostly of
zigzag (armchair) type edges exhibit antiferromagnetic (spin unpolarized)
states. In contrast, in situation of sublattice symmetry breaking, stable
ferri(o)magnetic states are obtained. For hydrogen-passivated nanomesh, the
formation energy is dramatically decreased, and ground state is found to
strongly depend on the vacancies shape and size. For triangular shaped holes,
the obtained net magnetic moments increase with the number difference of
removed A and B sites in agreement with Lieb's theorem for even A+B. For odd
A+B triangular meshes and all cases of non-triangular nanomeshes including the
one with even A+B, Lieb's theorem does not hold anymore which can be partially
attributed to introduction of armchair edges. In addition, large triangular
shaped GNM could be as robust as non-triangular GNMs, providing possible
solution to overcome one of crucial challenges for the sp-magnetism. Finally,
significant exchange splitting values as large as eV can be obtained
for highly asymmetric structures evidencing the potential of GNM for room
temperature carbon based spintronics. These results demonstrate that a turn
from 0-dimensional graphene nanoflakes throughout 1-dimensional graphene
nanoribbons with zigzag edges to GNM breaks localization of unpaired electrons
and provides deviation from the rules based on Lieb's theorem. Such
delocalization of the electrons leads the switch of the ground state of system
from antiferromagnetic narrow gap insulator discussed for graphene nanoribons
to ferromagnetic or nonmagnetic metal.Comment: 7 pages, 5 figures, 1 tabl
Performance Considerations of Network Functions Virtualization using Containers
The network performance of virtual machines plays a critical role in Network Functions Virtualization (NFV), and several technologies have been developed to address hardware-level virtualization shortcomings. Recent advances in operating system level virtualization and deployment platforms such as Docker have made containers an ideal candidate for high performance application encapsulation and deployment. However, Docker and other solutions typically use lower-performing networking mechanisms. In this paper, we explore the feasibility of using technologies designed to accelerate virtual machine networking with containers, in addition to quantifying the network performance of container-based VNFs compared to the state-of-the-art virtual machine solutions. Our results show that containerized applications can provide lower latency and delay variation, and can take advantage of high performance networking technologies previously only used for hardware virtualization
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) III. The Ultraviolet Source Catalogs
In this paper we introduce the deepest and most extensive ultraviolet
extragalactic source catalogs of the Virgo Cluster area to date. Archival and
targeted GALEX imaging is compiled and combined to provide the deepest possible
coverage over ~120 deg^2 in the NUV (lambda_eff=2316 angstroms) and ~40 deg^2
in the FUV (lambda_eff=1539 angstroms) between 180 deg <= R.A. <= 195 deg and 0
deg <= Decl. <= 20 deg. We measure the integrated photometry of 1770 extended
UV sources of all galaxy types and use GALEX pipeline photometry for 1,230,855
point-like sources in the foreground, within, and behind the cluster. Extended
source magnitudes are reliable to m_UV ~22, showing ~0.01 sigma difference from
their asymptotic magnitudes. Point-like source magnitudes have a 1 sigma
standard deviation within ~0.2 mag down to m_uv ~23. The point-like source
catalog is cross-matched with large optical databases and surveys including the
SDSS DR9 (> 1 million Virgo Cluster sources), the Next Generation Virgo Cluster
Survey (NGVS; >13 million Virgo Cluster sources), and the NED (~30,000 sources
in the Virgo Cluster). We find 69% of the entire UV point-like source catalog
has a unique optical counterpart, 11% of which are stars and 129 are Virgo
cluster members neither in the VCC nor part of the bright CGCG galaxy catalog
(i.e., m_pg < 14.5). These data are collected in four catalogs containing the
UV extended sources, the UV point-like sources, and two catalogs each
containing the most relevant optical parameters of UV-optically matched
point-like sources for further studies from SDSS and NGVS. The GUViCS catalogs
provide a unique set of data for future works on UV and multiwavelength studies
in the cluster and background environments.Comment: 35 pages, 24 figures, 15 tables, Accepted for publication in A&
The Next Generation Virgo Cluster Survey. VIII. The Spatial Distribution of Globular Clusters in the Virgo Cluster
We report on a large-scale study of the distribution of globular clusters
(GCs) throughout the Virgo cluster, based on photometry from the Next
Generation Virgo Cluster Survey, a large imaging survey covering Virgo's
primary subclusters to their virial radii. Using the g', (g'-i')
color-magnitude diagram of unresolved and marginally-resolved sources, we
constructed 2-D maps of the GC distribution. We present the clearest evidence
to date showing the difference in concentration between red and blue GCs over
the extent of the cluster, where the red (metal-rich) GCs are largely located
around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a
more extended spatial distribution, with significant populations present beyond
83' (215 kpc) along the major axes of M49 and M87. The GC distribution around
M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness
of the diffuse light surrounding both galaxies. We find evidence for spatial
enhancements of GCs surrounding M87 that may be indicative of recent
interactions or an ongoing merger history. We compare the GC map to the
locations of Virgo galaxies and the intracluster X-ray gas, and find good
agreement between these baryonic structures. The Virgo cluster contains a total
population of 6730014400 GCs, of which 35% are located in M87 and M49
alone. We compute a cluster-wide specific frequency S_N,CL=,
including Virgo's diffuse light. The GC-to-baryonic mass fraction is
e_b=and the GC-to-total cluster mass formation
efficiency is e_t=, values slightly lower than, but
consistent with, those derived for individual galactic halos. Our results show
that the production of the complex structures in the unrelaxed Virgo cluster
core (including the diffuse intracluster light) is an ongoing
process.(abridged)Comment: 23 pages, 17 figures. Accepted for publication in the Astrophysical
Journal. Figure 1 has reduced resolution. Revised version with updated
references, corrected typos -- no changes to result
Histone deacetylase inhibitors mitigate antipsychotic risperidone-induced motor side effects in aged mice and in a mouse model of Alzheimer’s disease
Antipsychotic drugs are still widely prescribed to control various severe neuropsychiatric symptoms in the elderly and dementia patients although they are off-label use in the United States. However, clinical practice shows greater side effects and lower efficacy of antipsychotics for this vulnerable population and the mechanisms surrounding this aged-related sensitivity are not well understood. Our previous studies have shown that aging-induced epigenetic alterations may be involved in the increasing severity of typical antipsychotic haloperidol induced side effects in aged mice. Still, it is unknown if similar epigenetic mechanisms extend to atypical antipsychotics, which are most often prescribed to dementia patients combined with severe neuropsychiatric symptoms. In this study, we report that atypical antipsychotic risperidone also causes increased motor side effect behaviors in aged mice and 5xFAD mice. Histone deacetylase (HDAC) inhibitor Valproic Acid and Entinostat can mitigate the risperidone induced motor side effects. We further showed besides D2R, reduced expression of 5-HT2A, one of the primary atypical antipsychotic targets in the striatum of aged mice that are also mitigated by HDAC inhibitors. Finally, we demonstrate that specific histone acetylation mark H3K27 is hypoacetylated at the 5htr2a and Drd2 promoters in aged mice and can be reversed with HDAC inhibitors. Our work here establishes evidence for a mechanism where aging reduces expression of 5-HT2A and D2R, the key atypical antipsychotic drug targets through epigenetic alteration. HDAC inhibitors can restore 5-HT2A and D2R expression in aged mice and decrease the motor side effects in aged and 5xFAD mice
The Next Generation Virgo Cluster Survey - Infrared (NGVS-IR): I. A new Near-UV/Optical/Near-IR Globular Cluster selection tool
The NGVS-IR project (Next Generation Virgo Survey - Infrared) is a contiguous
near-infrared imaging survey of the Virgo cluster of galaxies. It complements
the optical wide-field survey of Virgo (NGVS). The current state of NGVS-IR
consists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-band
imaging of 16 deg^2 covering the region between M49 and M87. In this paper, we
present the observations of the central 4 deg^2 centered on Virgo's core
region. The data were acquired with WIRCam on the Canada-France-Hawaii
Telescope and the total integration time was 41 hours distributed in 34
contiguous tiles. A survey-specific strategy was designed to account for
extended galaxies while still measuring accurate sky brightness within the
survey area. The average 5\sigma limiting magnitude is Ks=24.4 AB mag and the
50% completeness limit is Ks=23.75 AB mag for point source detections, when
using only images with better than 0.7" seeing (median seeing 0.54"). Star
clusters are marginally resolved in these image stacks, and Virgo galaxies with
\mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with optical
and ultraviolet data, we build the uiK color-color diagram which allows a very
clean color-based selection of globular clusters in Virgo. This diagnostic plot
will provide reliable globular cluster candidates for spectroscopic follow-up
campaigns needed to continue the exploration of Virgo's photometric and
kinematic sub-structures, and will help the design of future searches for
globular clusters in extragalactic systems. Equipped with this powerful new
tool, future NGVS-IR investigations based on the uiK diagram will address the
mapping and analysis of extended structures and compact stellar systems in and
around Virgo galaxies.Comment: 23 pages, 18 figures. Accepted for publication in ApJ
Towards Computational Models and Applications of Insect Visual Systems for Motion Perception: A Review
Motion perception is a critical capability determining a variety of aspects of insects' life, including avoiding predators, foraging and so forth. A good number of motion detectors have been identified in the insects' visual pathways. Computational modelling of these motion detectors has not only been providing effective solutions to artificial intelligence, but also benefiting the understanding of complicated biological visual systems. These biological mechanisms through millions of years of evolutionary development will have formed solid modules for constructing dynamic vision systems for future intelligent machines. This article reviews the computational motion perception models originating from biological research of insects' visual systems in the literature. These motion perception models or neural networks comprise the looming sensitive neuronal models of lobula giant movement detectors (LGMDs) in locusts, the translation sensitive neural systems of direction selective neurons (DSNs) in fruit flies, bees and locusts, as well as the small target motion detectors (STMDs) in dragonflies and hover flies. We also review the applications of these models to robots and vehicles. Through these modelling studies, we summarise the methodologies that generate different direction and size selectivity in motion perception. At last, we discuss about multiple systems integration and hardware realisation of these bio-inspired motion perception models
Room temperature chiral magnetic skyrmion in ultrathin magnetic nanostructures
Magnetic skyrmions are chiral spin structures with a whirling configuration.
Their topological properties, nanometer size and the fact that they can be
moved by small current densities have opened a new paradigm for the
manipulation of magnetisation at the nanoscale. To date, chiral skyrmion
structures have been experimentally demonstrated only in bulk materials and in
epitaxial ultrathin films and under external magnetic field or at low
temperature. Here, we report on the observation of stable skyrmions in
sputtered ultrathin Pt/Co/MgO nanostructures, at room temperature and zero
applied magnetic field. We use high lateral resolution X-ray magnetic circular
dichroism microscopy to image their chiral N\'eel internal structure which we
explain as due to the large strength of the Dzyaloshinskii-Moriya interaction
as revealed by spin wave spectroscopy measurements. Our results are
substantiated by micromagnetic simulations and numerical models, which allow
the identification of the physical mechanisms governing the size and stability
of the skyrmions.Comment: Submitted version. Extended version to appear in Nature
Nanotechnolog
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