We study the evolution of the hydrogen ionization field during the epoch of reionization (EoR) using seminumerical simulations. By calculating the Minkowski functionals (MFs) of the 21 cm brightness ...temperature field, which provides a quantitative description of topology of the neutral and ionized regions, we find that the reionization process can be divided into five stages, each with different topological structures, corresponding to isolated ionized regions ("bubbles"); connected ionized regions ("ionized fibers") that percolate through the cosmic volume; a sponge-like configuration with intertwined neutral and ionized regions after the overlap of bubbles; connected neutral regions ("neutral fibers"), when the ionized region begins to surround the remaining neutral region; and isolated neutral regions ("islands"), before the whole space is ionized except for the rare dense clumps in galaxies and minihalos and the reionization process is completed. We use the MFs and the size statistics on the ionized or neutral regions to distinguish these different stages and find the neutral fractions at which the transitions of the different stages occur. At the later stages of reionization the neutral regions are more isolated than the ionized regions; this is the motivation for the island model description of reionization. We compare the late-stage topological evolution in the island model and the bubble model, showing that in the island model the neutral fibers are more easily broken into multiple pieces owing to the ionizing background.
ABSTRACT
The Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) is the largest single-dish radio telescope in the world. In this paper, we make forecast on the FAST H i large-scale ...structure survey by mock observations. We consider a drift scan survey with the L-band 19 beam receiver, which may be commensal with the pulsar search and Galactic H i survey. We also consider surveys at lower frequency, using either the current single feed wide-band receiver or a future multibeam phased array feed (PAF) in the UHF band. We estimate the number density of detected H i galaxies and the measurement error in positions and the precision of the surveys are evaluated using both Fisher matrix and simulated observations. The measurement error in the H i galaxy power spectrum is estimated, and we find that the error is relatively large even at moderate redshifts, as the number of positively detected galaxies drops drastically with increasing redshift. However, good cosmological measurement could be obtained with the intensity mapping technique where the large scale H i distribution is measured without resolving individual galaxies. The figure of merit for the dark energy equation of state with different observation times is estimated, and we find that with the existing L-band multibeam receiver, a good measurement of low redshift large-scale structure can be obtained, which complements the existing optical surveys. With a PAF in the UHF band, the constraint can be much stronger, reaching the level of a dark energy task force stage IV experiment.
In this paper, event-triggered estimators are designed for discrete-time recurrent neural networks (RNNs) with unknown time-delay. Owing to the diversity and complexity of time-delays, it is ...difficult to accurately predict their information. Under the boundedness of activation functions, the delay-depend term is regarded as a bounded nonlinear disturbance. Two event-triggered estimators are designed to estimate the neuron states. The first one considers the case that the system states are subject to unknown time-delay, and the second one deals with the case that both the system states and measurement outputs are subject to unknown time-delay. The sufficient conditions are developed to guarantee the input-to-state practical stability of estimation error systems. Finally, the dynamic event-triggered strategy is introduced to further reduce the events. Two numerical examples are given to show the validity of the developed scheme.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Having higher capacity to undertake pressures and larger compensation ability compared with the U-shape bellows, toroidal or Ω-shape bellows are being more and more widely used in engineering. The ...wave-shape and wall thickness reduction of bellows are the most important parameters for measuring the hydroforming quality of the bellows. In order to provide references for actual manufacturing, it is valuable to study the factors influencing the hydroforming process and quality of the bellows. In this paper, finite element simulations of the hydroforming process of a monolayer and single-wave toroidal bellows and a two-layer and four-wave toroidal bellows were carried out. Stress and strain distributions before and after unloading were analyzed and the wave height and wall thickness reduction were examined. The numerical results were verified by the actual hydroforming measurements. In addition, ranges of the significant structural or operating factors for producing better bellows were studied and a formula to compute the wall thickness reduction was fitted based on the sufficient numerical results of the hydroforming simulations.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We present new radial velocity measurements from the Bulge Radial Velocity Assay, a large-scale spectroscopic survey of M-type giants in the Galactic bulge/bar region. The sample of ~4500 new radial ...velocities, mostly in the region -10degrees < l < +10degrees and b approximate -6degrees, more than doubles the existent published data set. Our new data extend our rotation curve and velocity dispersion profile to +20degrees which is ~2.8 kpc from the Galactic center. The new data confirm the cylindrical rotation observed at -6degrees and -8degrees and are an excellent fit to the Shen et al. N-body bar model. We measure the strength of the TiOvarepsilon molecular band as a first step toward a metallicity ranking of the stellar sample, from which we confirm the presence of a vertical abundance gradient. Our survey finds no strong evidence of previously unknown kinematic streams. We also publish our complete catalog of radial velocities, photometry, TiO band strengths, and spectra, which is available at the Infrared Science Archive as well as at UCLA.
Abstract
Knowing the conserved quantities that a galaxy’s stellar orbits conform to is important in helping us understand the stellar distribution and structures within the galaxy. Isolating ...integrals of motion and resonances are particularly important, non-isolating integrals less so. We compare the behavior and results of two methods for counting the number of conserved quantities, one based on the correlation integral approach and the other a more recent method using machine learning. Both methods use stellar orbit trajectories in phase space as their only input, and we create such trajectories from theoretical spherical, axisymmetric, and triaxial model galaxies. The orbits have known isolating integrals and resonances. We find that neither method is fully effective in recovering the numbers of these quantities, nor in determining the number of non-isolating integrals. From a computer performance perspective, we find the correlation integral approach to be the faster. Determining the algebraic formulae of (multiple) conserved quantities from the trajectories has not been possible due to the lack of an appropriate symbolic regression capability. Notwithstanding the shortcomings we have noted, it may be that the methods are usable as part of a trajectory analysis tool kit.
In this paper, local stability and Hopf bifurcation of a delayed heroin model with saturated treatment function are discussed. First of all, sufficient conditions for local stability and existence of ...Hopf bifurcation are obtained by regarding the time delay as a bifurcation parameter and analyzing the distribution of the roots of the associated characteristic equation. Directly afterward, properties of the Hopf bifurcation, such as the direction and stability, are investigated with the aid of the normal form theory and the manifold center theorem. Finally, numerical simulations are presented to justify the obtained theoretical results, and some suggestions are offered for controlling heroin abuse in populations.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great Observatories Origins Deep Survey to study the color-morphological properties of satellite galaxies and investigate ...possible alignment between the distribution of the satellites and the orientation of their central galaxy. We confirm the bimodal color and morphological-type distribution for satellite galaxies at this redshift range: the red and blue classes correspond to the early and late morphological types, respectively, and the early-type satellites are on average brighter than the late-type ones. Furthermore, there is a morphological conformity between the central and satellite galaxies: the fraction of early-type satellites in groups with an early-type central is higher than those with a late-type central galaxy. This effect is stronger at smaller separations from the central galaxy. We find a marginally significant signal of alignment between the major axis of the early-type central galaxy and its satellite system, while for the late-type centrals no significant alignment signal is found. We discuss the alignment signal in the context of shape evolution of groups.
Abstract
This work presents the initial results of the drift-scan observation for the neutral hydrogen (
Hi
) intensity mapping survey with the Five-hundred-meter Aperture Spherical radio Telescope ...(FAST). The data analyzed in this work were collected in night observations from 2019 through 2021. The primary findings are based on 28 hr of drift-scan observation carried out over 7 nights in 2021, which covers 60 deg
2
sky area. Our main findings are, first, our calibration strategy can successfully correct both the temporal and bandpass gain variation over the 4 hr drift-scan observation. Second, the continuum maps of the surveyed region are made with frequency resolution of 28 kHz and pixel area of
2.95
arcmin
2
. The pixel noise levels of the continuum maps are slightly higher than the forecast assuming
T
sys
= 20 K, which are 36.0 mK (for 10.0 s integration time) at the 1050–1150 MHz band, and 25.9 mK (for 16.7 s integration time) at the 1323–1450 MHz band, respectively. Third, the flux-weighted differential number count is consistent with the NRAO-VLA Sky Survey (NVSS) catalog down to the confusion limit ∼7 mJy beam
−1
. Finally, the continuum flux measurements of the sources are consistent with those found in the literature. The difference in the flux measurement of 81 isolated NVSS sources is about 6.3%. Our research offers a systematic analysis for the FAST
Hi
intensity mapping drift-scan survey and serves as a helpful resource for further cosmology and associated galaxies sciences with the FAST drift-scan survey.
This paper is concerned with the issue of adaptive synchronization for a general class of chaotic memristive competitive neural networks (MCNNs) with mixed time-varying delays and different time ...scales. By applying Lyapunov functional method and inequality analysis technique, a kind of novel adaptive controllers with feedback control laws are designed to achieve synchronization and exponential synchronization. The synchronization conditions , without need of excessive calculation such as solving linear matrix inequality or computing algebraic conditions, are given, which can be applied in MCNNs with different mathematical models of memristor proposed in the existing literature. Finally, an example with numerical simulations is listed to prove the efficiency and accuracy of the theoretical results.
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