26,384 research outputs found
Random graph model with power-law distributed triangle subgraphs
Clustering is well-known to play a prominent role in the description and
understanding of complex networks, and a large spectrum of tools and ideas have
been introduced to this end. In particular, it has been recognized that the
abundance of small subgraphs is important. Here, we study the arrangement of
triangles in a model for scale-free random graphs and determine the asymptotic
behavior of the clustering coefficient, the average number of triangles, as
well as the number of triangles attached to the vertex of maximum degree. We
prove that triangles are power-law distributed among vertices and characterized
by both vertex and edge coagulation when the degree exponent satisfies
; furthermore, a finite density of triangles appears as
.Comment: 4 pages, 2 figure; v2: major conceptual change
Ion exchange phase transitions in "doped" water--filled channels
Ion transport through narrow water--filled channels is impeded by a high
electrostatic barrier. The latter originates from the large ratio of the
dielectric constants of the water and a surrounding media. We show that
``doping'', i.e. immobile charges attached to the walls of the channel,
substantially reduces the barrier. This explains why most of the biological ion
channels are ``doped''. We show that at rather generic conditions the channels
may undergo ion exchange phase transitions (typically of the first order). Upon
such a transition a finite latent concentration of ions may either enter or
leave the channel, or be exchanged between the ions of different valences. We
discuss possible implications of these transitions for the Ca-vs.-Na
selectivity of biological Ca channels. We also show that transport of divalent
Ca ions is assisted by their fractionalization into two separate excitations.Comment: 16 pages, 27 figure
Quantum teleportation between moving detectors in a quantum field
We consider the quantum teleportation of continuous variables modeled by
Unruh-DeWitt detectors coupled to a common quantum field initially in the
Minkowski vacuum. An unknown coherent state of an Unruh-DeWitt detector is
teleported from one inertial agent (Alice) to an almost uniformly accelerated
agent (Rob, for relativistic motion), using a detector pair initially entangled
and shared by these two agents. The averaged physical fidelity of quantum
teleportation, which is independent of the observer's frame, always drops below
the best fidelity value from classical teleportation before the detector pair
becomes disentangled with the measure of entanglement evaluated around the
future lightcone of the joint measurement event by Alice. The distortion of the
quantum state of the entangled detector pair from the initial state can
suppress the fidelity significantly even when the detectors are still strongly
entangled around the lightcone. We point out that the dynamics of entanglement
of the detector pair observed in Minkowski frame or in quasi-Rindler frame are
not directly related to the physical fidelity of quantum teleportation in our
setup. These results are useful as a guide to making judicious choices of
states and parameter ranges and estimation of the efficiency of quantum
teleportation in relativistic quantum systems under environmental influences.Comment: 18 pages, 7 figure
Stabilizing quantum metastable states in a time-periodic potential
Metastability of a particle trapped in a well with a time-periodically
oscillating barrier is studied in the Floquet formalism. It is shown that the
oscillating barrier causes the system to decay faster in general. However,
avoided crossings of metastable states can occur with the less stable states
crossing over to the more stable ones. If in the static well there exists a
bound state, then it is possible to stabilize a metastable state by
adiabatically increasing the oscillating frequency of the barrier so that the
unstable state eventually cross-over to the stable bound state. It is also
found that increasing the amplitude of the oscillating field may change a
direct crossing of states into an avoided one.Comment: 7 pages, 6 figure
Ground-simulation investigations of VTOL airworthiness criteria for terminal-area operations
Several ground-based simulation experiments undertaken to investigate concerns related to tilt-rotor aircraft airworthiness were conducted. The experiments were conducted on the National Aeronautics and Space Administration (NASA) Ames Research Center's Vertical Motion Simulator, which permits simulation of a wide variety of aircraft with a high degree of fidelity of motion cueing. Variations in conversion/deceleration profile, type of augmentation or automation, level of display assistance, and meteorological conditions were considered in the course of the experiments. Certification pilots from the Federal Aviation Administration (FAA) and the Civil Aviation Authority (CAA) participated, in addition to NASA research pilots. The setup of these experiments on the simulator is summarized, and some of the results highlighted
Prospects from systems serology research
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142338/1/imm12861.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142338/2/imm12861_am.pd
Exact Master Equation and Quantum Decoherence of Two Coupled Harmonic Oscillators in a General Environment
In this paper we derive an exact master equation for two coupled quantum
harmonic oscillators interacting via bilinear coupling with a common
environment at arbitrary temperature made up of many harmonic oscillators with
a general spectral density function. We first show a simple derivation based on
the observation that the two-harmonic oscillator model can be effectively
mapped into that of a single harmonic oscillator in a general environment plus
a free harmonic oscillator. Since the exact one harmonic oscillator master
equation is available [Hu, Paz and Zhang, Phys. Rev. D \textbf{45}, 2843
(1992)], the exact master equation with all its coefficients for this two
harmonic oscillator model can be easily deduced from the known results of the
single harmonic oscillator case. In the second part we give an influence
functional treatment of this model and provide explicit expressions for the
evolutionary operator of the reduced density matrix which are useful for the
study of decoherence and disentanglement issues. We show three applications of
this master equation: on the decoherence and disentanglement of two harmonic
oscillators due to their interaction with a common environment under Markovian
approximation, and a derivation of the uncertainty principle at finite
temperature for a composite object, modeled by two interacting harmonic
oscillators. The exact master equation for two, and its generalization to ,
harmonic oscillators interacting with a general environment are expected to be
useful for the analysis of quantum coherence, entanglement, fluctuations and
dissipation of mesoscopic objects towards the construction of a theoretical
framework for macroscopic quantum phenomena.Comment: 35 pages, revtex, no figures, 2nd version, references added, to
appear in PR
Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals
Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD
Partially composite 2-Higgs-doublet model
In the extra dimensional scenarios with gauge fields in the bulk, the
Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type
attractive four-fermion interactions, which can break electroweak symmetry
dynamically with accompanying composite Higgs fields. We consider a possibility
that electroweak symmetry breaking (EWSB) is triggered by both a fundamental
Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism
induced by a new strong dynamics. The resulting Higgs sector is a partially
composite two-Higgs doublet model with specific boundary conditions on the
coupling and mass parameters originating at a compositeness scale .
The phenomenology of this model is discussed including the collider
phenomenology at LHC and ILC.Comment: To appear in the proceeding of LCWS06, Bangalore, Indi
Diameters in preferential attachment models
In this paper, we investigate the diameter in preferential attachment (PA-)
models, thus quantifying the statement that these models are small worlds. The
models studied here are such that edges are attached to older vertices
proportional to the degree plus a constant, i.e., we consider affine PA-models.
There is a substantial amount of literature proving that, quite generally,
PA-graphs possess power-law degree sequences with a power-law exponent \tau>2.
We prove that the diameter of the PA-model is bounded above by a constant
times \log{t}, where t is the size of the graph. When the power-law exponent
\tau exceeds 3, then we prove that \log{t} is the right order, by proving a
lower bound of this order, both for the diameter as well as for the typical
distance. This shows that, for \tau>3, distances are of the order \log{t}. For
\tau\in (2,3), we improve the upper bound to a constant times \log\log{t}, and
prove a lower bound of the same order for the diameter. Unfortunately, this
proof does not extend to typical distances. These results do show that the
diameter is of order \log\log{t}.
These bounds partially prove predictions by physicists that the typical
distance in PA-graphs are similar to the ones in other scale-free random
graphs, such as the configuration model and various inhomogeneous random graph
models, where typical distances have been shown to be of order \log\log{t} when
\tau\in (2,3), and of order \log{t} when \tau>3
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