7,990 research outputs found
Identifying influential spreaders and efficiently estimating infection numbers in epidemic models: a walk counting approach
We introduce a new method to efficiently approximate the number of infections
resulting from a given initially-infected node in a network of susceptible
individuals. Our approach is based on counting the number of possible infection
walks of various lengths to each other node in the network. We analytically
study the properties of our method, in particular demonstrating different forms
for SIS and SIR disease spreading (e.g. under the SIR model our method counts
self-avoiding walks). In comparison to existing methods to infer the spreading
efficiency of different nodes in the network (based on degree, k-shell
decomposition analysis and different centrality measures), our method directly
considers the spreading process and, as such, is unique in providing estimation
of actual numbers of infections. Crucially, in simulating infections on various
real-world networks with the SIR model, we show that our walks-based method
improves the inference of effectiveness of nodes over a wide range of infection
rates compared to existing methods. We also analyse the trade-off between
estimate accuracy and computational cost, showing that the better accuracy here
can still be obtained at a comparable computational cost to other methods.Comment: 6 page
Experimental Assessment on the Hysteretic Behavior of a Full-Scale Traditional Chinese Timber Structure Using a Synchronous Loading Technique
In traditional Chinese timber structures, few tie beams were used between columns, and the column base was placed directly on a stone base. In order to study the hysteretic behavior of such structures, a full-scale model was established. The model size was determined according to the requirements of an eighth grade material system specified in the architectural treatise Ying-zao-fa-shi written during the Song Dynasty. In light of the vertical lift and drop of the test model during horizontal reciprocating motions, the horizontal low-cycle reciprocating loading experiments were conducted using a synchronous loading technique. By analyzing the load-displacement hysteresis curves, envelope curves, deformation capacity, energy dissipation, and change in stiffness under different vertical loads, it is found that the timber frame exhibits obvious signs of self-restoring and favorable plastic deformation capacity. As the horizontal displacement increases, the equivalent viscous damping coefficient generally declines first and then increases. At the same time, the stiffness degrades rapidly first and then decreases slowly. Increasing vertical loading will improve the deformation, energy-dissipation capacity, and stiffness of the timber frame
Proportional and Preemption-enabled Traffic Offloading for IP Flow Mobility:Algorithms and Performance Evaluation
IP Flow Mobility (IFOM) enables a user equipment to offload data traffic at the IP flow level. Although the procedure of IFOM-based flow offloading has been specified by 3GPP, how many IP flows should be offloaded and when offloading should be performed are not defined. Consequently, IP flows may be routed to a target access network which has a strong signal strength but with backhaul congestion or insufficient access capability. In this paper, we propose two algorithms, referred to as proportional offloading (PO), and proportional and preemption-enabled offloading (PPO), respectively, for IP flow offloading in hybrid cellular and wireless local area networks. The PO algorithm decides an optimal proportion of IP flows which could be offloaded by considering available resources at the target access network. In the PPO algorithm, both service continuity and network utilization are taken into consideration. Furthermore, a detailed analytical model is developed in order to evaluate the behavior of the proposed algorithms. The analytical model is validated through extensive simulations. The results show that by dynamically adjusting the percentage of traffic flows to be offloaded, PO can reduce blocking probability and increase resource utilization. PPO further improves the performance at the cost of slightly higher offloading overhead
A right-handed isotropic medium with a negative refractive index
The sign of the refractive index of any medium is soley determined by the
requirement that the propagation of an electromagnetic wave obeys Einstein
causality. Our analysis shows that this requirement predicts that the real part
of the refractive index may be negative in an isotropic medium even if the
electric permittivity and the magnetic permeability are both positive. Such a
system may be a route to negative index media at optical frequencies. We also
demonstrate that the refractive index may be positive in left-handed media that
contain two molecular species where one is in its excited state.Comment: 4.1 pages, 4 figures, submitted to Physical Review Letter
Electron-phonon interaction dressed by electronic correlations near charge ordering as the origin for superconductivity in cobaltates
We consider possible routes to superconductivity in hydrated cobaltates
Na_xCoO_2.yH_2O on the basis of the t-J-V model plus phonons on the triangular
lattice. We studied the stability conditions for the homogeneous Fermi liquid
(HFL) phase against different broken symmetry phases. Besides the
sqrt(3)xsqrt(3)-CDW phase, triggered by the nearest-neighbour Coulomb
interaction V, we have found that the HFL is unstable, at very low doping,
against a bond-ordered phase due to J. We also discuss the occurrence of phase
separation at low doping and V. The interplay between the electron-phonon
interaction and correlations near the sqrt(3)xsqrt(3)-CDW leads to
superconductivity in the unconventional next-nearest neighbour f-wave (NNN-f)
channel with a dome shape for Tc around x ~ 0.35, and with values of a few
Kelvin as seen in experiments. Near the bond-ordered phase at low doping we
found tendencies to superconductivity with d-wave symmetry for finite J and
x<0.15. Contact with experiments is given along the paper.Comment: 21 pages, 6 figure
Comparison of Fatigue Performance between Additively Manufactured and Wrought 304L Stainless Steel using a Novel Fatigue Test Setup
In this research, a novel adaptive controlled fatigue testing machine was designed for bending type high cycle fatigue test. A unique dual gauge section Krouse type mini specimen was designed for simply supported transverse bending. Displacement controlled fatigue tests were implemented using an electromechanical actuator. The variation in the control signal and load observed during the test provides unique insights into realizing the deterioration of the specimen due to fatigue. These analyses were utilized to compare the fatigue performance of wrought and additively manufactured 304L stainless steel. The influence of the build direction on fatigue performance was also investigated by testing specimens with 0, 45, and 90 degrees build direction. These comparisons were carried out at different levels of displacement amplitude
Fabrication and Characterization of AlₓCoFeNiCu₁₋ₓ High Entropy Alloys by Laser Metal Deposition
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