20,054 research outputs found
Progress on tilted axis cranking covariant density functional theory for nuclear magnetic and antimagnetic rotation
Magnetic rotation and antimagnetic rotation are exotic rotational phenomena
observed in weakly deformed or near-spherical nuclei, which are
respectivelyinterpreted in terms of the shears mecha-nism and two shearslike
mechanism. Since their observations, magnetic rotation and antimagnetic
rotation phenomena have been mainly investigated in the framework of tilted
axis cranking based on the pairing plus quadrupole model. For the last decades,
the covariant density functional theory and its extension have been proved to
be successful in describing series of nuclear ground-states and excited states
properties, including the binding energies, radii, single-particle spectra,
resonance states, halo phenomena, magnetic moments, magnetic rotation,
low-lying excitations, shape phase transitions, collective rotation and
vibrations, etc. This review will mainly focus on the tilted axis cranking
covariant density functional theory and its application for the magnetic
rotation and antimagnetic rotation phenomena.Comment: 53 pages, 19 figure
Antimagnetic Rotation Band in Nuclei: A Microscopic Description
Covariant density functional theory and the tilted axis cranking method are
used to investigate antimagnetic rotation (AMR) in nuclei for the first time in
a fully self-consistent and microscopic way. The experimental spectrum as well
as the B(E2) values of the recently observed AMR band in 105Cd are reproduced
very well. This gives a further strong hint that AMR is realized in specific
bands in nuclei.Comment: 10 pages, 4 figure
The Carnegie-Irvine Galaxy Survey. III. The Three-Component Structure of Nearby Elliptical Galaxies
Motivated by recent developments in our understanding of the formation and
evolution of massive galaxies, we explore the detailed photometric structure of
a representative sample of 94 bright, nearby elliptical galaxies, using
high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample
spans a range of environments and stellar masses, from M* = 10^{10.2} to
10^{12.0} solar mass. We exploit the unique capabilities of two-dimensional
image decomposition to explore the possibility that local elliptical galaxies
may contain photometrically distinct substructure that can shed light on their
evolutionary history. Compared with the traditional one-dimensional approach,
these two-dimensional models are capable of consistently recovering the surface
brightness distribution and the systematic radial variation of geometric
information at the same time. Contrary to conventional perception, we find that
the global light distribution of the majority (>75%) of elliptical galaxies is
not well described by a single Sersic function. Instead, we propose that local
elliptical galaxies generically contain three subcomponents: a compact (R_e < 1
kpc) inner component with luminosity fraction f ~ 0.1-0.15; an
intermediate-scale (R_e ~ 2.5 kpc) middle component with f ~ 0.2-0.25; and a
dominant (f = 0.6), extended (R_e ~ 10 kpc) outer envelope. All subcomponents
have average Sersic indices n ~ 1-2, significantly lower than the values
typically obtained from single-component fits. The individual subcomponents
follow well-defined photometric scaling relations and the stellar mass-size
relation. We discuss the physical nature of the substructures and their
implications for the formation of massive elliptical galaxies.Comment: To appear in The Astrophysical Journal; 36 pages, 2 tables, 38
figures; For the full resolution version, see:
http://users.obs.carnegiescience.edu/shuang/PaperIII.pdf ; For the atlas of
all selected models, see
http://users.obs.carnegiescience.edu/shuang/AppendixE.pd
The Carnegie-Irvine Galaxy Survey. IV. A Method to Determine the Average Mass Ratio of Mergers That Built Massive Elliptical Galaxies
Many recent observations and numerical simulations suggest that nearby
massive, early-type galaxies were formed through a "two-phase" process. In the
proposed second phase, the extended stellar envelope was accumulated through
many dry mergers. However, details of the past merger history of present-day
ellipticals, such as the typical merger mass ratio, are difficult to constrain
observationally. Within the context and assumptions of the two-phase formation
scenario, we propose a straightforward method, using photometric data alone, to
estimate the average mass ratio of mergers that contributed to the build-up of
massive elliptical galaxies. We study a sample of nearby massive elliptical
galaxies selected from the Carnegie-Irvine Galaxy Survey, using two-dimensional
analysis to decompose their light distribution into an inner, denser component
plus an extended, outer envelope, each having a different optical color. The
combination of these two substructures accurately recovers the negative color
gradient exhibited by the galaxy as whole. The color difference between the two
components ( ~ 0.10 mag; ~ 0.14 mag), based on the
slope of the M_stellar-color relation for nearby early-type galaxies, can be
translated into an estimate of the average mass ratio of the mergers. The rough
estimate, 1:5 to 1:10, is consistent with the expectation of the two-phase
formation scenario, suggesting that minor mergers were largely responsible for
building up to the outer stellar envelope of present-day massive ellipticals.
With the help of accurate photometry, large sample size, and more choices of
colors promised by ongoing and future surveys, the approach proposed here can
reveal more insights into the growth of massive galaxies during the last few
Gyr.Comment: Accepted by ApJ; 20 pages, 11 figures, 1 table; The high resolution
figures and the full table can be downloaded from here:
https://github.com/dr-guangtou/cgs_colorgra
Some statistical properties of spiral galaxies
This paper presents some statistical correlations of 72 northern spiralgalaxies. The results show that early-type spirals that are brighter, andthicker, and the axis ratios () of the disk tend to be smaller alongthe Hubble sequence. We also find that correlates strongly with thegalaxy's color, and early-type spirals have larger values of . Theinclinations obtained by fitting the pattern of a spiral structure with alogarithmic spiral form are nearly the same as those obtained by using theformulas of Aaronson et al. (1980). Finally, the mean measured pitch angles forthe different Hubble sequences in the Third Catalogue of Bright Galaxies by deVaucouleurs et al. (1991) are derived
Effective photon mass in nuclear matter and finite nuclei
Electromagnetic field in nuclear matter and nuclei are studied. In the
nuclear matter, because the expectation value of the electric charge density
operator is not zero, different in vacuum, the U(1) local gauge symmetry of
electric charge is spontaneously broken, and consequently, the photon gains an
effective mass through the Higgs mechanism. An alternative way to study the
effective mass of photon is to calculate the self-energy of photon
perturbatively. It shows that the effective mass of photon is about
in the symmetric nuclear matter at the saturation density and about at the surface of . It seems that
the two-body decay of a massive photon causes the sharp lines of
electron-positron pairs in the low energy heavy ion collision experiments of
.Comment: 10 pages, 2 figures, 1 table, REVTEX4, submitted to Int. J. Mod.
Phys.
Networked Control Systems: The Communication Basics and Control Methodologies
As an emerging research field, networked control systems have shown the increasing importance and attracted more and more attention in the recent years. The integration of control and communication in networked control systems has made the design and analysis of such systems a great theoretical challenge for conventional control theory. Such an integration also makes the implementation of networked control systems a necessary intermediate step towards the final convergence of control, communication, and computation. We here introduce the basics of networked control systems and then describe the state-of-the-art research in this field. We hope such a brief tutorial can be useful to inspire further development of networked control systems in both theory and potential applications
- …