Semiflows and intrinsic shape in topological spaces

In this paper we apply the intrinsic approach to shape to study attractors in topological spaces.

Phase Evolution of the Time- and Space-Like Peregrine Breather in a Laboratory

Coherent wave groups are not only characterized by the intrinsic shape of the wave packet, but also by the underlying phase evolution during the propagation. Exact deterministic formulations of hydrodynamic or electromagnetic coherent wave groups can be obtained by solving the nonlinear Schrödinger equation (NLSE). When considering the NLSE, there are two asymptotically equivalent formulations, which can be used to describe the wave dynamics: the time- or space-like NLSE. These differences have been theoretically elaborated upon in the 2016 work of Chabchoub and Grimshaw. In this paper, we address fundamental characteristic differences beyond the shape of wave envelope, which arise in the phase evolution. We use the Peregrine breather as a referenced wave envelope model, whose dynamics is created and tracked in a wave flume using two boundary conditions, namely as defined by the time- and space-like NLSE. It is shown that whichever of the two boundary conditions is used, the corresponding local shape of wave localization is very close and almost identical during the evolution; however, the respective local phase evolution is different. The phase dynamics follows the prediction from the respective NLSE framework adopted in each case.

A Fast Point Clouds Registration Algorithm for Laser Scanners

Point clouds registration is an important step for laser scanner data processing, and there have been numerous methods. However, the existing methods often suffer from low accuracy and low speed when registering large point clouds. To meet this challenge, an improved iterative closest point (ICP) algorithm combining random sample consensus (RANSAC) algorithm, intrinsic shape signatures (ISS), and 3D shape context (3DSC) is proposed. The proposed method firstly uses voxel grid filter for down-sampling. Next, the feature points are extracted by the ISS algorithm and described by the 3DSC. Afterwards, the ISS-3DSC features are used for rough registration with the RANSAC algorithm. Finally, the ICP algorithm is used for accurate registration. The experimental results show that the proposed algorithm has faster registration speed than the compared algorithms, while maintaining high registration accuracy.

Evolution of disc thickness in simulated high-redshift galaxies

ABSTRACT We study the growth of stellar discs of Milky Way-sized galaxies using a suite of cosmological simulations. We calculate the half-mass axis lengths and axis ratios of stellar populations split by age in galaxies with stellar mass $M_{*}=10^7\!-\!10^{10}\, \mathrm{M}_{\odot }$ at redshifts z > 1.5. We find that in our simulations stars always form in relatively thin discs, and at ages below 100 Myr are contained within half-mass height z1/2 ∼ 0.1 kpc and short-to-long axial ratio z1/2/x1/2 ∼ 0.15. Disc thickness increases with the age of stellar population, reaching median z1/2 ∼ 0.8 kpc and z1/2/x1/2 ∼ 0.6 for stars older than 500 Myr. We trace the same group of stars over the simulation snapshots and show explicitly that their intrinsic shape grows more spheroidal over time. We identify a new mechanism that contributes to the observed disc thickness: rapid changes in the orientation of the galactic plane mix the configuration of young stars. The frequently mentioned ‘upside-down’ formation scenario of galactic discs, which posits that young stars form in already thick discs at high redshift, may be missing this additional mechanism of quick disc inflation. The actual formation of stars within a fairly thin plane is consistent with the correspondingly flat configuration of dense molecular gas that fuels star formation.

Control of septum thickness by the curvature of SepF polymers

Gram-positive bacteria divide by forming a thick cross wall. How the thickness of this septal wall is controlled is unknown. In this type of bacteria, the key cell division protein FtsZ is anchored to the cell membrane by two proteins, FtsA and/or SepF. We have isolated SepF homologs from different bacterial species and found that they all polymerize into large protein rings with diameters varying from 19 to 44 nm. Interestingly, these values correlated well with the thickness of their septa. To test whether ring diameter determines septal thickness, we tried to construct different SepF chimeras with the purpose to manipulate the diameter of the SepF protein ring. This was indeed possible and confirmed that the conserved core domain of SepF regulates ring diameter. Importantly, when SepF chimeras with different diameters were expressed in the bacterial hostBacillus subtilis, the thickness of its septa changed accordingly. These results strongly support a model in which septal thickness is controlled by curved molecular clamps formed by SepF polymers attached to the leading edge of nascent septa. This also implies that the intrinsic shape of a protein polymer can function as a mold to shape the cell wall.

The stellar halos of ETGs in the IllustrisTNG simulations: The photometric and kinematic diversity of galaxies at large radii

Context. Early-type galaxies (ETGs) are found to follow a wide variety of merger and accretion histories in cosmological simulations. Aims. We characterize the photometric and kinematic properties of simulated ETG stellar halos, and compare them to the observations. Methods. We selected a sample of 1114 ETGs in the TNG100 simulation and 80 in the higher-resolution TNG50. These ETGs span a stellar mass range of 1010.3 − 1012 M⊙ and they were selected within the range of g − r colour and λ-ellipticity diagram populated by observed ETGs. We determined photometric parameters, intrinsic shapes, and kinematic observables in their extended stellar halos. We compared the results with central IFU kinematics and ePN.S planetary nebula velocity fields at large radii, studying the variation in kinematics from center to halo, and connecting it to a change in the intrinsic shape of the galaxies. Results. We find that the simulated galaxy sample reproduces the diversity of kinematic properties observed in ETG halos. Simulated fast rotators (FRs) divide almost evenly in one third having flat λ profiles and high halo rotational support, a third with gently decreasing profiles, and another third with low halo rotation. However, the peak of rotation occurs at larger R than in observed ETG samples. Slow rotators (SRs) tend to have increased rotation in the outskirts, with half of them exceeding λ = 0.2. For M* > 1011.5 M⊙ halo rotation is unimportant. A similar variety of properties is found for the stellar halo intrinsic shapes. Rotational support and shape are deeply related: the kinematic transition to lower rotational support is accompanied by a change towards rounder intrinsic shape. Triaxiality in the halos of FRs increases outwards and with stellar mass. Simulated SRs have relatively constant triaxiality profiles. Conclusions. Simulated stellar halos show a large variety of structural properties, with quantitative but no clear qualitative differences between FRs and SRs. At the same stellar mass, stellar halo properties show a more gradual transition and significant overlap between the two families, despite the clear bimodality in the central regions. This is in agreement with observations of extended photometry and kinematics.

Weak lensing measurement of filamentary structure with the SDSS BOSS and Subaru Hyper Suprime-Cam data

ABSTRACT We report the weak lensing measurement of filaments between Sloan Digital Sky Survey (SDSS) III/Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxy pairs at z ∼ 0.55, using the Subaru Hyper Suprime-Cam (HSC) first-year galaxy shape catalogue. Despite of the small overlap of 140 deg2 between these surveys, we detect the filament lensing signal at 3.9σ significance, which is the highest signal-to-noise lensing measurement of filaments between galaxy-scale haloes at this redshift range. We derive a theoretical prediction and covariance using mock catalogues based on full-sky ray-tracing simulations. We find that the intrinsic scatter of filament properties and the fluctuations in a large-scale structure along the line of sight are the primary component of the covariance and the intrinsic shape noise from source galaxies no longer limits our lensing measurement. This fact demonstrates the statistical power of the HSC survey due to its deep observations and high number density of source galaxies. Our result is consistent with the theoretical prediction and supports the ‘thick’ filament model. As the HSC survey area increases, we will be able to study detailed filament properties such as the dark matter distributions and redshift evolution of filaments.

Separating the intrinsic alignment signal and the lensing signal using self-calibration in photo-z surveys with KiDS450 and KV450 Data

ABSTRACT To reach the full potential for the next generation of weak lensing surveys, it is necessary to mitigate the contamination of intrinsic alignments (IAs) of galaxies in the observed cosmic shear signal. The self-calibration (SC) of IAs provides an independent method to measure the IA signal from the survey data and the photometric redshift information. It operates differently from the marginalization method based on the IA modelling. In this work, we present the first application of SC to the KiDS450 data and the KV450 data, to split directly the intrinsic shape–galaxy density (Ig) correlation signal and the gravitational shear–galaxy density (Gg) correlation signal, using the information from photometric redshift (photo-z). We achieved a clear separation of the two signals and performed several validation tests. Our measured signals are found to be in general agreement with the KiDS450 cosmic shear best-fitting cosmology, for both lensing and IA measurements. For KV450, we use partial (high-z) data, and our lensing measurements are also in good agreement with KV450 cosmic shear best fit, while our IA signal suggests a larger IA amplitude for the high-z sample. We discussed the impact of photo-z quality on IA detection and several other potential systematic biases. Finally, we discuss the potential application of the information extracted for both the lensing signal and the IA signal in future surveys.