10,056 research outputs found
Correlation Between the Halo Concentration (c) and the Virial Mass (Mvir) Determined from X-ray Clusters
Numerical simulations of structure formation have suggested that there exists
a good correlation between the halo concentration c (or the characteristic
density delta_c) and the virial mass Mvir for any virialized dark halo
described by the Navarro, Frenk & White (1995) density profile. In this Letter,
we present an observational determination of the c-Mvir (or delta_c-Mvir)
relation in the mass range of 10^14< Mvir <10^16 (solar mass) using a sample of
63 X-ray luminous clusters. The best-fit power law relation, which is roughly
independent of the values of Omega_M and Lambda, is c propto Mvir^(-0.5) or
delta_c propto Mvir^(-1.2), indicating n=-0.7 for a scale-free power spectrum
of the primordial density fluctuations. We discuss the possible reasons for the
conflict with the predictions by typical CDM models such as SCDM, LCDM and
OCDM.Comment: 13 pages, 1 figure, two tables. Accepted for publication in ApJ
The relationship between metabolic rate and sociability is altered by food-deprivation
Individuals vary in the extent to which they associate with conspecifics, but little is known about the energetic underpinnings of this variation in sociability. Group-living allows individuals to find food more consistently, but within groups, there can be competition for food items. Individuals with an increased metabolic rate could display decreased sociability to reduce competition. Long-term food deprivation (FD) may alter any links between sociability and metabolic rate by affecting motivation to find food.
We examined these issues in juvenile qingbo carp Spinibarbus sinensis, to understand how FD and metabolic rate affect sociability. Like many aquatic ectotherms, this species experiences seasonal bouts of FD.
Individuals were either: (i) food-deprived for 21 days; or (ii) fed a maintenance ration (control). Fish from each treatment were measured for standard metabolic rate (SMR) and tested for sociability twice: once in the presence of a control stimulus shoal and once with a food-deprived stimulus shoal.
Control individuals ventured further from stimulus shoals over a 30-min trial, while food-deprived fish did not change their distance from stimulus shoals as trials progressed. Control fish with a higher SMR were least sociable. Well-fed controls showed decreased sociability when exposed to food-deprived stimulus shoals, but there was evidence of consistency in relative sociability between exposures to different shoal types.
Results contrast with previous findings that several days of fasting causes individuals to decrease associations with conspecifics. Prolonged FD may cause individuals to highly prioritize food acquisition, and the decreased vigilance that would accompany continuous foraging may heighten the need for the antipredator benefits of shoaling. Conversely, decreased sociability in well-fed fish with a high SMR probably minimizes intraspecific competition, allowing them to satisfy an increased energetic demand while foraging. Together, these results suggest that FD â a challenge common for many ectothermic species â can affect individual sociability as well as the attractiveness of groups towards conspecifics. In addition, the lack of a link between SMR and sociability in food-deprived fish suggests that, in situations where group membership is linked to fitness, the extent of correlated selection on metabolic traits may be context-dependent
In an Attempt to Introduce Long-range Interactions into Small-world Networks
Distinguishing the long-range bonds with the regular ones, the critical
temperature of the spin-lattice Guassian model built on two typical Small-world
Networks (SWNs) is studied. The results show much difference from the classical
case, and thus may induce some more accurate discussion on the critical
properties of the spin-lattice systems combined with the SWNs.Comment: 4 pages, 3 figures, 18 referenc
The Effect of Radiative Cooling on the Sunyaev-Zel'dovich Cluster Counts and Angular Power Spectrum: Analytic Treatment
Recently, the entropy excess detected in the central cores of groups and
clusters has been successfully interpreted as being due to radiative cooling of
the hot intragroup/intracluster gas. In such a scenario, the entropy floors
in groups/clusters at any given redshift are completely
determined by the conservation of energy. In combination with the equation of
hydrostatic equilibrium and the universal density profile for dark matter, this
allows us to derive the remaining gas distribution of groups and clusters after
the cooled material is removed. Together with the Press-Schechter mass function
we are able to evaluate effectively how radiative cooling can modify the
predictions of SZ cluster counts and power spectrum. It appears that our
analytic results are in good agreement with those found by hydrodynamical
simulations. Namely, cooling leads to a moderate decrease of the predicted SZ
cluster counts and power spectrum as compared with standard scenario. However,
without taking into account energy feedback from star formation which may
greatly suppress cooling efficiency, it is still premature to claim that this
modification is significant for the cosmological applications of cluster SZ
effect.Comment: 16 pages, 3 figures, uses aastex.cls. ApJ accepte
Contamination of Cluster Radio Sources in the Measurement of the Thermal Sunyaev-Zel'dovich Angular Power Spectrum
We present a quantitative estimate of the confusion of cluster radio halos
and galaxies in the measurement of the angular power spectrum of the thermal
Sunyaev-Zel'dovich (SZ) effect. To achieve the goal, we use a purely analytic
approach to both radio sources and dark matter of clusters by incorporating
empirical models and observational facts together with some theoretical
considerations. It is shown that the correction of cluster radio halos and
galaxies to the measurement of the thermal SZ angular power spectrum is no more
than 20% at for observing frequencies GHz. This eliminates
the concern that the SZ measurement may be seriously contaminated by the
existence of cluster radio sources.Comment: 15 pages, 3 figures, accepted for publication in Ap
Relative entropy of entanglement of a kind of two qubit entangled states
We in this paper strictly prove that some block diagonalizable two qubit
entangled state with six none zero elements reaches its quantum relative
entropy entanglement by the a separable state having the same matrix structure.
The entangled state comprises local filtering result state as a special case.Comment: 5 page
Entanglement and quantum phase transition in the one-dimensional anisotropic XY model
In this paper the entanglement and quantum phase transition of the
anisotropic s=1/2 XY model are studied by using the quantum renormalization
group method. By solving the renormalization equations, we get the trivial
fixed point and the untrivial fixed point which correspond to the phase of the
system and the critical point, respectively. Then the concurrence between two
blocks are calculated and it is found that when the number of the iterations of
the renormalziation trends infinity, the concurrence develops two staturated
values which are associated with two different phases, i.e., Ising-like and
spin-fluid phases. We also investigate the first derivative of the concurrence,
and find that there exists non-analytic behaviors at the quantum critical
point, which directly associate with the divergence of the correlation length.
Further insight, the scaling behaviors of the system are analyzed, it is shown
that how the maximum value of the first derivative of the concurrence reaches
the infinity and how the critical point is touched as the size of the system
becomes large.Comment: 10 pages, 5 figure
Interlayer pair tunneling and gap anisotropy in YBaCuO
Recent ARPES measurement observed a large -axis gap anisotropy,
, in clean YBaCuO. This
indicates that some sub-dominant component may exist in the -wave
dominant gap. We propose that the interlayer pairing tunneling contribution can
be determined through the investigation of the order parameter anisotropy.
Their potentially observable features in transport and spin dynamics are also
studied.Comment: 4 pages, 3 figure
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