1,627 research outputs found
Size distribution of galaxies in SDSS DR7: weak dependence on halo environment
Using a sample of galaxies selected from the Sloan Digital Sky Survey Data
Release 7 (SDSS DR7) and a catalog of bulge-disk decompositions, we study how
the size distribution of galaxies depends on the intrinsic properties of
galaxies, such as concentration, morphology, specific star formation rate
(sSFR), and bulge fraction, and on the large-scale environments in the context
of central/satellite decomposition, halo environment, the cosmic web: \cluster,
\filament, \sheet ~and \void, as well as galaxy number density. We find that
there is a strong dependence of the luminosity- or mass-size relation on the
galaxy concentration, morphology, sSFR, and bulge fraction. Compared with
late-type (spiral) galaxies, there is a clear trend of smaller sizes and
steeper slope for early-type (elliptical) galaxies. Similarly, galaxies with
high bulge fraction have smaller sizes and steeper slope than those with low
bulge fraction. Fitting formula of the average luminosity- and mass-size
relations are provided for galaxies of these different intrinsic properties.
Examining galaxies in terms of their large scale environments, we find that the
mass-size relation has some weak dependence on the halo mass and
central/satellite segregation for galaxies within mass range , where satellites or galaxies in more massive halos have
slightly smaller sizes than their counterparts. While the cosmic web and local
number density dependence of the mass-size relation is almost negligible.Comment: 12 pages, 11 figure
Towards a Simple Relationship to Estimate the Capacity of Static and Mobile Wireless Networks
Extensive research has been done on studying the capacity of wireless
multi-hop networks. These efforts have led to many sophisticated and customized
analytical studies on the capacity of particular networks. While most of the
analyses are intellectually challenging, they lack universal properties that
can be extended to study the capacity of a different network. In this paper, we
sift through various capacity-impacting parameters and present a simple
relationship that can be used to estimate the capacity of both static and
mobile networks. Specifically, we show that the network capacity is determined
by the average number of simultaneous transmissions, the link capacity and the
average number of transmissions required to deliver a packet to its
destination. Our result is valid for both finite networks and asymptotically
infinite networks. We then use this result to explain and better understand the
insights of some existing results on the capacity of static networks, mobile
networks and hybrid networks and the multicast capacity. The capacity analysis
using the aforementioned relationship often becomes simpler. The relationship
can be used as a powerful tool to estimate the capacity of different networks.
Our work makes important contributions towards developing a generic methodology
for network capacity analysis that is applicable to a variety of different
scenarios.Comment: accepted to appear in IEEE Transactions on Wireless Communication
Using member galaxy luminosities as halo mass proxies of galaxy groups
Reliable halo mass estimation for a given galaxy system plays an important
role both in cosmology and galaxy formation studies. Here we set out to find
the way that can improve the halo mass estimation for those galaxy systems with
limited brightest member galaxies been observed. Using four mock galaxy samples
constructed from semi-analytical formation models, the subhalo abundance
matching method and the conditional luminosity functions, respectively, we find
that the luminosity gap between the brightest and the subsequent brightest
member galaxies in a halo (group) can be used to significantly reduce the
scatter in the halo mass estimation based on the luminosity of the brightest
galaxy alone. Tests show that these corrections can significantly reduce the
scatter in the halo mass estimations by to in massive
halos depending on which member galaxies are considered. Comparing to the
traditional ranking method, we find that this method works better for groups
with less than five members, or in observations with very bright magnitude cut.Comment: ApJ accepte
A New Cell Association Scheme In Heterogeneous Networks
Cell association scheme determines which base station (BS) and mobile user
(MU) should be associated with and also plays a significant role in determining
the average data rate a MU can achieve in heterogeneous networks. However, the
explosion of digital devices and the scarcity of spectra collectively force us
to carefully re-design cell association scheme which was kind of taken for
granted before. To address this, we develop a new cell association scheme in
heterogeneous networks based on joint consideration of the
signal-to-interference-plus-noise ratio (SINR) which a MU experiences and the
traffic load of candidate BSs1. MUs and BSs in each tier are modeled as several
independent Poisson point processes (PPPs) and all channels experience
independently and identically distributed ( i.i.d.) Rayleigh fading. Data rate
ratio and traffic load ratio distributions are derived to obtain the tier
association probability and the average ergodic MU data rate. Through numerical
results, We find that our proposed cell association scheme outperforms cell
range expansion (CRE) association scheme. Moreover, results indicate that
allocating small sized and high-density BSs will improve spectral efficiency if
using our proposed cell association scheme in heterogeneous networks.Comment: Accepted by IEEE ICC 2015 - Next Generation Networking Symposiu
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