1,729 research outputs found
The Centaurus Group and the Outer Halo of NGC 5128: Are they Dynamically Connected?
NGC 5128, a giant elliptical galaxy only Mpc away, is the dominant
member of a galaxy group of over 80 probable members. The Centaurus group
provides an excellent sample for a kinematic comparison between the halo of NGC
5128 and its surrounding satellite galaxies. A new study, presented here, shows
no kinematic difference in rotation amplitude, rotation axis, and velocity
dispersion between the halo of NGC 5128, determined from over of its
globular clusters, and those of the Centaurus group as a whole. These results
suggest NGC 5128 could be behaving in part as the inner component to the galaxy
group, and could have begun as a large initial seed galaxy, gradually built up
by minor mergers and satellite accretions, consistent with simple cold dark
matter models. The mass and mass-to-light ratios in the B-band, corrected for
projection effects, are determined to be
M_{\sun} and M_{\sun}/L_{\sun} for NGC 5128 out to a
galactocentric radius of 45 kpc, and M_{\sun}
and M_{\sun}/L_{\sun} for the Centaurus group, consistent with
previous studies.Comment: 14 pages, 3 tables, 7 figures, Accepted for publication in A
A Circuit Model for Domain Walls in Ferromagnetic Nanowires: Application to Conductance and Spin Transfer Torques
We present a circuit model to describe the electron transport through a
domain wall in a ferromagnetic nanowire. The domain wall is treated as a
coherent 4-terminal device with incoming and outgoing channels of spin up and
down and the spin-dependent scattering in the vicinity of the wall is modelled
using classical resistances. We derive the conductance of the circuit in terms
of general conductance parameters for a domain wall. We then calculate these
conductance parameters for the case of ballistic transport through the domain
wall, and obtain a simple formula for the domain wall magnetoresistance which
gives a result consistent with recent experiments. The spin transfer torque
exerted on a domain wall by a spin-polarized current is calculated using the
circuit model and an estimate of the speed of the resulting wall motion is
made.Comment: 10 pages, 5 figures; submitted to Physical Review
Theory of scanning gate microscopy
A systematic theory of the conductance measurements of non-invasive (weak
probe) scanning gate microscopy is presented that provides an interpretation of
what precisely is being measured. A scattering approach is used to derive
explicit expressions for the first and second order conductance changes due to
the perturbation by the tip potential in terms of the scattering states of the
unperturbed structure. In the case of a quantum point contact, the first order
correction dominates at the conductance steps and vanishes on the plateaus
where the second order term dominates. Both corrections are non-local for a
generic structure. Only in special cases, such as that of a centrally symmetric
quantum point contact in the conductance quantization regime, can the second
order correction be unambiguously related with the local current density. In
the case of an abrupt quantum point contact we are able to obtain analytic
expressions for the scattering eigenfunctions and thus evaluate the resulting
conductance corrections.Comment: 19 pages, 7 figure
Inclination-Independent Galaxy Classification
We present a new method to classify galaxies from large surveys like the
Sloan Digital Sky Survey using inclination-corrected concentration,
inclination-corrected location on the color-magnitude diagram, and apparent
axis ratio. Explicitly accounting for inclination tightens the distribution of
each of these parameters and enables simple boundaries to be drawn that
delineate three different galaxy populations: Early-type galaxies, which are
red, highly concentrated, and round; Late-type galaxies, which are blue, have
low concentrations, and are disk dominated; and Intermediate-type galaxies,
which are red, have intermediate concentrations, and have disks. We have
validated our method by comparing to visual classifications of high-quality
imaging data from the Millennium Galaxy Catalogue. The inclination correction
is crucial to unveiling the previously unrecognized Intermediate class.
Intermediate-type galaxies, roughly corresponding to lenticulars and early
spirals, lie on the red sequence. The red sequence is therefore composed of two
distinct morphological types, suggesting that there are two distinct mechanisms
for transiting to the red sequence. We propose that Intermediate-type galaxies
are those that have lost their cold gas via strangulation, while Early-type
galaxies are those that have experienced a major merger that either consumed
their cold gas, or whose merger progenitors were already devoid of cold gas
(the ``dry merger'' scenario).Comment: Accepted for publication in ApJ. 7 pages in emulateap
TCR-Signaling Events in Cellular Metabolism and Specialization
Engaging the T cell receptor (TCR) with peptide:MHC complexes initiates a cascade of signaling events that activates T cells in an antigen specific manner. It is now clear that multiple inputs, including the strength of TCR signaling, co-stimulation, and the cytokine environment, impact T cell specialization decisions in the context of specific pathogenic encounters. Additionally, it is now appreciated that these same stimuli direct cellular metabolism programs. In this review, we will discuss how TCR-signaling events coordinate cellular metabolism and specialization gene programs in T cells
Voxel-Based Indoor Reconstruction From HoloLens Triangle Meshes
Current mobile augmented reality devices are often equipped with range
sensors. The Microsoft HoloLens for instance is equipped with a Time-Of-Flight
(ToF) range camera providing coarse triangle meshes that can be used in custom
applications. We suggest to use the triangle meshes for the automatic
generation of indoor models that can serve as basis for augmenting their
physical counterpart with location-dependent information. In this paper, we
present a novel voxel-based approach for automated indoor reconstruction from
unstructured three-dimensional geometries like triangle meshes. After an
initial voxelization of the input data, rooms are detected in the resulting
voxel grid by segmenting connected voxel components of ceiling candidates and
extruding them downwards to find floor candidates. Semantic class labels like
'Wall', 'Wall Opening', 'Interior Object' and 'Empty Interior' are then
assigned to the room voxels in-between ceiling and floor by a rule-based voxel
sweep algorithm. Finally, the geometry of the detected walls and their openings
is refined in voxel representation. The proposed approach is not restricted to
Manhattan World scenarios and does not rely on room surfaces being planar.Comment: 8 pages, 4 figure
Normal classification of 3D occupancy grids for voxel-based indoor reconstruction from point clouds
In this paper, we present an automated method for classification of binary voxel occupancy grids of discretized indoor mapping data such as point clouds or triangle meshes according to normal vector directions. Filled voxels get assigned normal class labels distinguishing between horizontal and vertical building structures. The horizontal building structures are further differentiated into those with normal directions pointing upwards or downwards with respect to the building interior. The derived normal grids can be deployed in the context of an existing voxel-based indoor reconstruction pipeline, which so far was only applicable to indoor mapping triangle meshes that already contain normal vectors consistently oriented with respect to the building interior. By means of quantitative evaluation against reference data, we demonstrate the performance of the proposed method and its applicability in the context of voxel-based indoor reconstruction from indoor mapping point clouds without normal vectors. The code of our implementation is made available to the public at https://github.com/huepat/voxir
Residual Shuffling Convolutional Neural Networks for Deep Semantic Image Segmentation Using Multi-Modal Data
In this paper, we address the deep semantic segmentation of aerial imagery based on multi-modal data. Given multi-modal data composed of true orthophotos and the corresponding Digital Surface Models (DSMs), we extract a variety of hand-crafted radiometric and geometric features which are provided separately and in different combinations as input to a modern deep learning framework. The latter is represented by a Residual Shuffling Convolutional Neural Network (RSCNN) combining the characteristics of a Residual Network with the advantages of atrous convolution and a shuffling operator to achieve a dense semantic labeling. Via performance evaluation on a benchmark dataset, we analyze the value of different feature sets for the semantic segmentation task. The derived results reveal that the use of radiometric features yields better classification results than the use of geometric features for the considered dataset. Furthermore, the consideration of data on both modalities leads to an improvement of the classification results. However, the derived results also indicate that the use of all defined features is less favorable than the use of selected features. Consequently, data representations derived via feature extraction and feature selection techniques still provide a gain if used as the basis for deep semantic segmentation
Length-dependent oscillations of the conductance through atomic chains: The importance of electronic correlations
We calculate the conductance of atomic chains as a function of their length.
Using the Density Matrix Renormalization Group algorithm for a many-body model
which takes into account electron-electron interactions and the shape of the
contacts between the chain and the leads, we show that length-dependent
oscillations of the conductance whose period depends on the electron density in
the chain can result from electron-electron scattering alone. The amplitude of
these oscillations can increase with the length of the chain, in contrast to
the result from approaches which neglect the interactions.Comment: 7 pages, 4 figure
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