23,088 research outputs found
Assortative Mixing Equilibria in Social Network Games
It is known that individuals in social networks tend to exhibit homophily
(a.k.a. assortative mixing) in their social ties, which implies that they
prefer bonding with others of their own kind. But what are the reasons for this
phenomenon? Is it that such relations are more convenient and easier to
maintain? Or are there also some more tangible benefits to be gained from this
collective behaviour?
The current work takes a game-theoretic perspective on this phenomenon, and
studies the conditions under which different assortative mixing strategies lead
to equilibrium in an evolving social network. We focus on a biased preferential
attachment model where the strategy of each group (e.g., political or social
minority) determines the level of bias of its members toward other group
members and non-members. Our first result is that if the utility function that
the group attempts to maximize is the degree centrality of the group,
interpreted as the sum of degrees of the group members in the network, then the
only strategy achieving Nash equilibrium is a perfect homophily, which implies
that cooperation with other groups is harmful to this utility function. A
second, and perhaps more surprising, result is that if a reward for inter-group
cooperation is added to the utility function (e.g., externally enforced by an
authority as a regulation), then there are only two possible equilibria,
namely, perfect homophily or perfect heterophily, and it is possible to
characterize their feasibility spaces. Interestingly, these results hold
regardless of the minority-majority ratio in the population.
We believe that these results, as well as the game-theoretic perspective
presented herein, may contribute to a better understanding of the forces that
shape the groups and communities of our society
Experimental investigation on thermal comfort model between local thermal sensation and overall thermal sensation
To study the human local and overall thermal sensations, a series of experiments under various conditions were carried out in a climate control chamber. The adopted analysis method considered the effect of the weight coefficient of local average skin temperature and density of the cold receptors’ distribution in different local body areas. The results demonstrated that the thermal sensation of head, chest, back and hands is warmer than overall thermal sensation. The mean thermal sensation votes of those local areas were more densely distributed. In addition, the thermal sensation of arms, tight and calf was colder than the overall thermal sensation, which pronounced that thermal sensation votes were more dispersed. The thermal sensation of chest and back had a strong linear correlation with overall thermal sensation. Considering the actual scope of air-conditioning regulation, the human body was classified into three local parts: a) head, b) upper part of body and c) lower part of body. The prediction model of both the three-part thermal sensation and overall thermal sensation was developed. Weight coefficients were 0.21, 0.60 and 0.19 respectively. The model provides scientist basis for guiding the sage installation place of the personal ventilation system to achieve efficient energy use
Observational Evidence for an Age Dependence of Halo Bias
We study the dependence of the cross-correlation between galaxies and galaxy
groups on group properties. Confirming previous results, we find that the
correlation strength is stronger for more massive groups, in good agreement
with the expected mass dependence of halo bias. We also find, however, that for
groups of the same mass, the correlation strength depends on the star formation
rate (SFR) of the central galaxy: at fixed mass, the bias of galaxy groups
decreases as the SFR of the central galaxy increases. We discuss these findings
in light of the recent findings by Gao et al (2005) that halo bias depends on
halo formation time, in that halos that assemble earlier are more strongly
biased. We also discuss the implication for galaxy formation, and address a
possible link to galaxy conformity, the observed correlation between the
properties of satellite galaxies and those of their central galaxy.Comment: 4 pages, 4 figures, Accepted for publication in ApJ Letters. Figures
3 and 4 replaced. The bias dependence on the central galaxy luminosity is
omitted due to its sensitivity to the mass mode
Independent Orbiter Assessment (IOA): FMEA/CIL assessment
The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. Direction was given by the Orbiter and GFE Projects Office to perform the hardware analysis and assessment using the instructions and ground rules defined in NSTS 22206. The IOA analysis features a top-down approach to determine hardware failure modes, criticality, and potential critical items. To preserve independence, the anlaysis was accomplished without reliance upon the results contained within the NASA and prime contractor FMEA/CIL documentation. The assessment process compares the independently derived failure modes and criticality assignments to the proposed NASA Post 51-L FMEA/CIL documentation. When possible, assessment issues are discussed and resolved with the NASA subsystem managers. The assessment results for each subsystem are summarized. The most important Orbiter assessment finding was the previously unknown stuck autopilot push-button criticality 1/1 failure mode, having a worst case effect of loss of crew/vehicle when a microwave landing system is not active
Internet source evaluation: The role of implicit associations and psychophysiological self-regulation
This study focused on middle school students\u2019 source evaluation skills as a key component of digital literacy. Specifically, it examined the role of two unexplored individual factors that may affect the evaluation of sources providing information about the controversial topic of the health risks associated with the use of mobile phones. The factors were the implicit association of mobile phone with health or no health, and psychophysiological self-regulation as reflected in basal Heart Rate Variability (HRV). Seventy-two seventh graders read six webpages that provided contrasting information on the unsettled topic of the potential health risks related to the use of mobile phones. Then they were asked to rank-order the six websites along the dimension of reliability (source evaluation). Findings revealed that students were able to discriminate between the most and least reliable websites, justifying their ranking in light of different criteria. However, overall, they were little accurate in rank-ordering all six Internet sources. Both implicit associations and HRV correlated with source evaluation. The interaction between the two individual variables was a significant predictor of participants\u2019 performance in rank-ordering the websites for reliability. A slope analysis revealed that when students had an average psychophysiological self-regulation, the stronger their association of the mobile phone with health, the better their performance on source evaluation. Theoretical and educational significances of the study are discussed
Angular separations of the lensed QSO images
We have analyzed the observed image separations of the gravitationally lensed
images of QSOs for a possible correlation with the source redshift. Contrary to
the previously noted anti-correlation based on a smaller data set, no
correlation is found for the currently available data. We have calculated the
average image separations of the lensed QSOs as a function of source redshifts,
for isothermal spheres with cores in a flat universe, taking into account the
amplification bias caused by lensing. The shape of the distribution of average
image separation as a function of redshift is very robust and is insensitive to
most model parameters. Observations are found to be roughly consistent with the
theoretical results for models which assume the lens distribution to be (i)
Schechter luminosity function which, however, can not produce images with large
separation and (ii) the mass condensations in a cold dark matter universe, as
given by the Press-Schechter theory if an upper limit of 1-7
M is assumed on the mass of the condensations.Comment: 20 pages, 7 postscript figures, accepted for publication in The
Astrophysical Journa
Imprint of Inhomogeneous Reionization on the Power Spectrum of Galaxy Surveys at High Redshifts
We consider the effects of inhomogeneous reionization on the distribution of
galaxies at high redshifts. Modulation of the formation process of the ionizing
sources by large scale density modes makes reionization inhomogeneous and
introduces a spread to the reionization times of different regions with the
same size. After sources photo-ionize and heat these regions to a temperature
\ga 10^4K at different times, their temperatures evolve as the ionized
intergalactic medium (IGM) expands. The varying IGM temperature makes the
minimum mass of galaxies spatially non-uniform with a fluctuation amplitude
that increases towards small scales. These scale-dependent fluctuations modify
the shape of the power spectrum of low-mass galaxies at high redshifts in a way
that depends on the history of reionization. The resulting distortion of the
primordial power spectrum is significantly larger than changes associated with
uncertainties in the inflationary parameters, such as the spectral index of the
scalar power spectrum or the running of the spectral index. Future surveys of
high-redshift galaxies will offer a new probe of the thermal history of the IGM
but might have a more limited scope in constraining inflation.Comment: 8 pages, 5 figures, replaced to match version accepted by Ap
Galaxy Groups in the SDSS DR4: II. halo occupation statistics
We investigate various halo occupation statistics using a large galaxy group
catalogue constructed from the SDSS DR4 with an adaptive halo-based group
finder. The conditional luminosity function (CLF) is measured separately for
all, red and blue galaxies, as well as in terms of central and satellite
galaxies. The CLFs for central and satellite galaxies can be well modelled with
a log-normal distribution and a modified Schechter form, respectively. About
85% of the central galaxies and about 80% of the satellite galaxies in halos
with masses M_h\ga 10^{14}\msunh are red galaxies. These numbers decrease to
50% and 40%, respectively, in halos with M_h \sim 10^{12}\msunh. For halos of
a given mass, the distribution of the luminosities of central galaxies, ,
has a dispersion of about 0.15 dex. The mean luminosity (stellar mass) of the
central galaxies scales with halo mass as
() for halos with masses M\gg 10^{12.5}\msunh, and
both relations are significantly steeper for less massive halos. We also
measure the luminosity (stellar mass) gap between the first and second
brightest (most massive) member galaxies, (). These gap statistics, especially in halos with M_h \la
10^{14.0}\msunh, indicate that the luminosities of central galaxies are
clearly distinct from those of their satellites. The fraction of fossil groups,
defined as those groups with , ranges from for groups with M_h\sim 10^{14}\msunh to 18-60% for groups with
M_h\sim 10^{13}\msunh. Finally, we measure the fraction of satellites, which
changes from for galaxies with \rmag\sim -22.0 to for
galaxies with \rmag\sim -17.0. (abridged)Comment: 16 pages, 11 figures. Accepted for publication in Ap
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Deformation and mechanical properties of the expansive cements produced by inter-grinding cement clinker and MgOs with various reactivities
Magnesia (MgO) either intrinsically contained in cement clinker or prepared separately as expansive
additive has been used to compensate for the shrinkage of cementitious materials. In this study, for
improving the homogenous distribution of MgOs, the cement clinker was inter-ground with MgO expansive
additives with various reactivities ranging from 50 to 400 s to prepare series of expansive Portland
cements and blended cements with incorporation of slag and fly ash. The deformations and mechanical
properties of the expansive cements were investigated. Results showed that the expansive cements containing
more reactive MgOs produced more rapid expansion under sealed condition or water curing, leading
to effective autogenous shrinkage compensations at early age. The reactivities of MgOs caused
insignificant influences on the mechanical strengths of expansive cements. The blended cements had
lower strengths at early age but higher strengths than that of the corresponding Portland cements at late
age due to the pozzolanic reaction.The financial support from the Royal Academy of Engineering
UK/China, India Exchange, The National Key Technology R&D Program
(2011BAE27B01-1), Priority Academic Program Development
of Jiangsu Higher Education Institutions (PAPD), and National Natural
Science Foundation of China (51461135003) are acknowledged.This is the accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0950061815000914#
Mesoscopic colonization of a spectral band
We consider the unitary matrix model in the limit where the size of the
matrices become infinite and in the critical situation when a new spectral band
is about to emerge. In previous works the number of expected eigenvalues in a
neighborhood of the band was fixed and finite, a situation that was termed
"birth of a cut" or "first colonization". We now consider the transitional
regime where this microscopic population in the new band grows without bounds
but at a slower rate than the size of the matrix. The local population in the
new band organizes in a "mesoscopic" regime, in between the macroscopic
behavior of the full system and the previously studied microscopic one. The
mesoscopic colony may form a finite number of new bands, with a maximum number
dictated by the degree of criticality of the original potential. We describe
the delicate scaling limit that realizes/controls the mesoscopic colony. The
method we use is the steepest descent analysis of the Riemann-Hilbert problem
that is satisfied by the associated orthogonal polynomials.Comment: 17 pages, 2 figures, minor corrections and addition
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