52 research outputs found
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Effect of end-wall riblets on radial turbine performance
This paper presents a detailed study of the impact of manufacturing residual riblets at the rotor hub surface of a radial inflow turbine on the flow within the rotor passages and their contribution to drag reduction. Numerical analysis has been used to study the effects of those features at design point conditions. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. The relative height of the riblets to rotor inlet blade height was introduced to generalise the results. At the end of this study the results were compared with the available data in literature. It was found that the introduction of riblets could reduce the wall shear stress at the hub surface, while they contribute to increasing the streamwise vorticity within the rotor passage. For the geometries tested, the minimum drag was achieved using riblets with relative height hrel = 2.5% equivalent to 19.3 wall units. The results revealed that the spacing between riblets have a minor effect on their performance, this is due to the size of the streamwise vortex above the hub surface which will be discussed in this work
Convergence to SPDEs in Stratonovich form
We consider the perturbation of parabolic operators of the form
by large-amplitude highly oscillatory spatially dependent
potentials modeled as Gaussian random fields. The amplitude of the potential is
chosen so that the solution to the random equation is affected by the
randomness at the leading order. We show that, when the dimension is smaller
than the order of the elliptic pseudo-differential operator , the
perturbed parabolic equation admits a solution given by a Duhamel expansion.
Moreover, as the correlation length of the potential vanishes, we show that the
latter solution converges in distribution to the solution of a stochastic
parabolic equation with a multiplicative term that should be interpreted in the
Stratonovich sense. The theory of mild solutions for such stochastic partial
differential equations is developed. The behavior described above should be
contrasted to the case of dimensions that are larger than or equal to the order
of the elliptic pseudo-differential operator . In the latter case, the
solution to the random equation converges strongly to the solution of a
homogenized (deterministic) parabolic equation as is shown in the companion
paper [2]. The stochastic model is therefore valid only for sufficiently small
space dimensions in this class of parabolic problems.Comment: 21 page
Oscillatory Fractional Brownian Motion and Hierarchical Random Walks
We introduce oscillatory analogues of fractional Brownian motion,
sub-fractional Brownian motion and other related long range dependent Gaussian
processes, we discuss their properties, and we show how they arise from
particle systems with or without branching and with different types of initial
conditions, where the individual particle motion is the so-called c-random walk
on a hierarchical group. The oscillations are caused by the discrete and
ultrametric structure of the hierarchical group, and they become slower as time
tends to infinity and faster as time approaches zero. We also give other
results to provide an overall picture of the behavior of this kind of systems,
emphasizing the new phenomena that are caused by the ultrametric structure as
compared with results for analogous models on Euclidean space
Human antibodies targeting Zika virus NS1 provide protection against disease in a mouse model.
Zika virus is a mosquito-borne flavivirus closely related to dengue virus that can cause severe disease in humans, including microcephaly in newborns and Guillain-Barré syndrome in adults. Specific treatments and vaccines for Zika virus are not currently available. Here, we isolate and characterize four monoclonal antibodies (mAbs) from an infected patient that target the non-structural protein NS1. We show that while these antibodies are non-neutralizing, NS1-specific mAbs can engage FcγR without inducing antibody dependent enhancement (ADE) of infection in vitro. Moreover, we demonstrate that mAb AA12 has protective efficacy against lethal challenges of African and Asian lineage strains of Zika virus in Stat2-/- mice. Protection is Fc-dependent, as a mutated antibody unable to activate known Fc effector functions or complement is not protective in vivo. This study highlights the importance of the ZIKV NS1 protein as a potential vaccine antigen
Necessary and sufficient condition for the smoothness of intersection local time of subfractional Brownian motions
A stochastic epidemic model of COVID-19 disease
To model the evolution of diseases with extended latency periods and the presence of asymptomatic patients like COVID-19, we define a simple discrete time stochastic SIR-type epidemic model. We include both latent periods as well as the presence of quarantine areas, to capture the evolutionary dynamics of such diseases
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