Betweenness centrality correlation in social networks

Scale-free (SF) networks exhibiting a power-law degree distribution can be grouped into the assortative, dissortative and neutral networks according to the behavior of the degree-degree correlation coefficient. Here we investigate the betweenness centrality (BC) correlation for each type of SF networks. While the BC-BC correlation coefficients behave similarly to the degree-degree correlation coefficients for the dissortative and neutral networks, the BC correlation is nontrivial for the assortative ones found mainly in social networks. The mean BC of neighbors of a vertex with BC $g_i$ is almost independent of $g_i$, implying that each person is surrounded by almost the same influential environments of people no matter how influential the person is.Comment: 4 pages, 4 figures, 1 tabl

Absorption cross section in warped AdS_3 black hole revisited

We investigate the absorption cross section for minimal-coupled scalars in the warped AdS_3 black hole. According to our calculation, the cross section reduces to the horizon area in the low energy limit as usually expected in contrast to what was previously found. We also calculate the greybody factor and find that the effective temperatures for the two chiral CFT's are consistent with that derived from the quasinormal modes. Observing the conjectured warped AdS/CFT correspondence, we suspect that a specific sector of the CFT operators with the desired conformal dimension could be responsible for the peculiar thermal behaviour of the warped AdS_3 black hole.Comment: 16+1 pages, typos corrected, references and footnotes adde

Higher Derivative CP(N) Model and Quantization of the Induced Chern-Simons Term

We consider higher derivative CP(N) model in 2+1 dimensions with the Wess-Zumino-Witten term and the topological current density squared term. We quantize the theory by using the auxiliary gauge field formulation in the path integral method and prove that the extended model remains renormalizable in the large N limit. We find that the Maxwell-Chern-Simons theory is dynamically induced in the large N effective action at a nontrivial UV fixed point. The quantization of the Chern-Simons term is also discussed.Comment: 8 pages, no figure, a minor change in abstract, added Comments on the quantization of the Chern-Simons term whose coefficient is also corrected, and some references are added. Some typos are corrected. Added a new paragraph checking the equivalence between (3) and (5), and a related referenc

Sufficiency Criterion for the Validity of the Adiabatic Approximation

We examine the quantitative condition which has been widely used as a criterion for the adiabatic approximation but was recently found insufficient. Our results indicate that the usual quantitative condition is sufficient for a special class of quantum mechanical systems. For general systems, it may not be sufficient, but it along with additional conditions is sufficient. The usual quantitative condition and the additional conditions constitute a general criterion for the validity of the adiabatic approximation, which is applicable to all $N-$dimensional quantum systems. Moreover, we illustrate the use of the general quantitative criterion in some physical models.Comment: 9 pages, no figure,appearing in PRL98(2007)15040

Observation of Competing Order in a High-TcT_{c} Superconductor with Femtosecond Optical Pulses

We present studies of the photoexcited quasiparticle dynamics in Tl$_{2}$Ba$_{2}$Ca$_{2}$Cu$_{3}$O$_{y}$ (Tl-2223) using femtosecond optical techniques. Deep into the superconducting state (below 40 K), a dramatic change occurs in the temporal dynamics associated with photoexcited quasiparticles rejoining the condensate. This is suggestive of entry into a coexistence phase which, as our analysis reveals, opens a gap in the density of states (in addition to the superconducting gap), and furthermore, competes with superconductivity resulting in a depression of the superconducting gap.Comment: 5 pages, 3 figure

Entanglement between qubits induced by a common environment with a gap

We study a system of two qubits interacting with a common environment, described by a two-spin boson model. We demonstrate two competing roles of the environment: inducing entanglement between the two qubits and making them decoherent. For the environment of a single harmonic oscillator, if its frequency is commensurate with the induced two-qubit coupling strength, the two qubits could be maximally entangled and the environment could be separable. In the case of the environment of a bosonic bath, the gap of its spectral density function is essential to generate entanglement between two qubits at equilibrium and for it to be used as a quantum data bus.Comment: accepted for publication in Physical Review

Electronic States in Diffused Quantum Wells

In the present study we calculate the energy values and the spatial distributions of the bound electronic states in some diffused quantum wells. The calculations are performed within the virtual crystal approximation, $sp^3 s^*$ spin dependent empirical tight-binding model and the surface Green function matching method. A good agreement is found between our results and experimental data obtained for AlGaAs/GaAs quantum wells with thermally induced changes in the profile at the interfaces. Our calculations show that for diffusion lengths $L_{D}=20\div100$ {\AA} the transition (C3-HH3) is not sensitive to the diffusion length, but the transitions (C1-HH1), (C1-LH1), (C2-HH2) and (C2-LH2) display large "blue shifts" as L_{D} increases. For diffusion lengths $L_{D}=0\div20$ {\AA} the transitions (C1-HH1) and (C1-LH1) are less sensitive to the L_{D} changes than the (C3-HH3) transition. The observed dependence is explained in terms of the bound states spatial distributions.Comment: ReVTeX file, 7pp., no macros, 4 figures available on the reques

Classification of scale-free networks

While the emergence of a power law degree distribution in complex networks is intriguing, the degree exponent is not universal. Here we show that the betweenness centrality displays a power-law distribution with an exponent \eta which is robust and use it to classify the scale-free networks. We have observed two universality classes with \eta \approx 2.2(1) and 2.0, respectively. Real world networks for the former are the protein interaction networks, the metabolic networks for eukaryotes and bacteria, and the co-authorship network, and those for the latter one are the Internet, the world-wide web, and the metabolic networks for archaea. Distinct features of the mass-distance relation, generic topology of geodesics and resilience under attack of the two classes are identified. Various model networks also belong to either of the two classes while their degree exponents are tunable.Comment: 6 Pages, 6 Figures, 1 tabl

Absorption cross section in the topologically massive gravity at the critical point

The absorption cross section for the the warped AdS$_3$ black hole background shows that it is larger than the area even if the s-wave limit is considered. It raises some question whether the deviation from the areal cross section is due to the warped configuration of the geometry or the rotating coordinate system, where these two effects are mixed up in the warped AdS$_3$ black hole. So, we study the low-frequency scattering dynamics of propagating scalar fields under the warped AdS$_3$ background at the critical point which reduces to the BTZ black hole in the rotating frame without the warped factor, which shows that the deformation effect at the critical point does not appear.Comment: 12 pages, LaTe