4,331 research outputs found
Impact of delay on HIV-1 dynamics of fighting a virus with another virus
In this paper, we propose a mathematical model for HIV-1 infection with
intracellular delay. The model examines a viral-therapy for controlling
infections through recombining HIV-1 virus with a genetically modified virus.
For this model, the basic reproduction number are identified
and its threshold properties are discussed. When , the
infection-free equilibrium is globally asymptotically stable. When
, becomes unstable and there occurs the
single-infection equilibrium , and and exchange their
stability at the transcritical point . If , where is a positive constant explicitly depending on the model
parameters, is globally asymptotically stable, while when , loses its stability to the double-infection equilibrium .
There exist a constant such that is asymptotically stable if
, and and exchange their stability at the
transcritical point . We use one numerical example to
determine the largest range of for the local stability of
and existence of Hopf bifurcation. Some simulations are performed to support
the theoretical results. These results show that the delay plays an important
role in determining the dynamic behaviour of the system. In the normal range of
values, the delay may change the dynamic behaviour quantitatively, such as
greatly reducing the amplitudes of oscillations, or even qualitatively changes
the dynamical behaviour such as revoking oscillating solutions to equilibrium
solutions. This suggests that the delay is a very important fact which should
not be missed in HIV-1 modelling
On the turbulent flow models in modelling of omni-flow wind turbine
Yong Chen, Pei Ying, Yigeng Xu, Yuan Tian, 'On the turbulent flow models in modelling of omni-flow wind turbine', paper presented at The International Conference on Next Generation Wind Energy (ICNGWE2014), the Universidad Europa de Madrid, Madrid, Spain, 7th-10th October 2014.The computational fluid dynamics (CFD) has a wide application in the wind energy industry. In CFD simulations, a turbulence model plays a significantly important role in accuracy and resource cost. In this paper, a novel wind turbine, omni-flow wind turbine, was investigated with different turbulence models. Four turbulence models, standard k-ε, realizable k-ε, standard k-ω and SST k-ω models, were employed for this wind turbine in order to assess the best numerical configuration. The performance of these four turbulence models was validated with wind tunnel tests. It is evident that the realizable k-ε turbulence model is most suitable to simulate this novel wind turbine
UV-finite scalar field theory with unitarity
In this paper we show how to define the UV completion of a scalar field
theory such that it is both UV-finite and perturbatively unitary. In the UV
completed theory, the propagator is an infinite sum of ordinary propagators. To
eliminate the UV divergences, we choose the coefficients and masses in the
propagator to satisfy certain algebraic relations, and define the infinite sums
involved in Feynman diagram calculation by analytic continuation. Unitarity can
be proved relatively easily by Cutkosky's rules. The theory is equivalent to
infinitely many particles with specific masses and interactions. We take the
theory as an example and demonstrate our idea through explicit Feynman
diagram computation.Comment: 14 pages, references adde
Thermodynamics of percolation in interacting systems
Interacting systems can be studied as the networks where nodes are system
units and edges denote correlated interactions. Although percolation on network
is a unified way to model the emergence and propagation of correlated
behaviours, it remains unknown how the dynamics characterized by percolation is
related to the thermodynamics of phase transitions. It is non-trivial to
formalize thermodynamics for most complex systems, not to mention calculating
thermodynamic quantities and verifying scaling relations during percolation. In
this work, we develop a formalism to quantify the thermodynamics of percolation
in interacting systems, which is rooted in a discovery that percolation
transition is a process for the system to lose the freedom degrees associated
with ground state configurations. We derive asymptotic formulas to accurately
calculate entropy and specific heat under our framework, which enables us to
detect phase transitions and demonstrate the Rushbrooke equality (i.e.,
) in six representative complex systems (e.g.,
Bernoulli and bootstrap percolation, classical and quantum synchronization,
non-linear oscillations with damping, and cellular morphogenesis). These
results suggest the general applicability of our framework in analyzing diverse
interacting systems and percolation processes
High-contrast coronagraph for ground-based imaging of Jupiter-like planets
We propose a high-contrast coronagraph for direct imaging of young
Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a
step-transmission filter in which the intensity is apodized with a finite
number of steps of identical transmission in each step. It should be installed
on a large ground-based telescope equipped with state-of-the-art adaptive
optics systems. In that case, contrast ratios around 10^-6 should be accessible
within 0.1 arc seconds of the central star. In recent progress, a coronagraph
with circular apodizing filter has been developing, which can be used for a
ground-based telescope with central obstruction and spider structure. It is
shown that ground-based direct imaging of Jupiter-like planets is promising
with current technology
Computational and Experimental Investigations of an Omni-Flow Wind Turbine
This document is the Accepted Manuscript version, made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License CC BY NC-ND 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/ ). The final, definitive version of this paper is available online at doi: https://doi.org/10.1016/j.apenergy.2015.01.067.Both numerical and experimental studies were conducted to evaluate the performance of an omni-flow wind turbine designed to provide renewable electricity on the top of urban buildings like skyscrapers. The numerical approach was based on Finite Volume Method (FVM) and the turbulence flow was studied with several commonly used Reynolds-averaged Navier–Stokes turbulence models. The results of the study were evaluated with the wind tunnel test results over a range of tip speed ratios. The numerical results showed the effect of blade number on both power output and starting capability. Although both the power and torque coefficient were improved significantly by the optimisation of the blade number, there was only a slight change when the blade number was greater than twenty. The results from wind tunnel testing also showed excellent starting capability with a starting wind velocity as low as 1.6 m/s. A numerical simulation was also conducted for the wind turbine working under non-uniform flow conditions. The numerical results have shown that the peak power coefficient of such a wind turbine under non-uniform flow, was lower than that under the uniform flow. Additionally, the applied thrust on a blade was subject to frequent and periodical changes. However, the effect of the change of thrust in magnitude and frequency was not significant. Therefore the omni-flow wind turbine has the potential to meet the challenge of unpredictable wind velocity and direction as a consequence of the urban environment.Peer reviewedFinal Accepted Versio
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