635 research outputs found
The Population Biology and Transmission Dynamics of Loa loa
Endemic to Central Africa, loiasis – or African eye worm (caused by the filarial nematode Loa loa) – affects more than 10 million people. Despite causing ocular and systemic symptoms, it has typically been considered a benign condition, only of public health relevance because it impedes mass drug administration-based interventions against onchocerciasis and lymphatic filariasis in co-endemic areas. Recent research has challenged this conception, demonstrating excess mortality associated with high levels of infection, implying that loiasis warrants attention as an intrinsic public health problem. This review summarises available information on the key parasitological, entomological, and epidemiological characteristics of the infection and argues for the mobilisation of resources to control the disease, and the development of a mathematical transmission model to guide deployment of interventions
Co-infection with Onchocerca volvulus and Loa loa microfilariae in central Cameroon: are these two species interacting?
Ivermectin treatment may induce severe adverse reactions in some individuals heavily infected with Loa loa. This hampers the implementation of mass ivermectin treatment against onchocerciasis in areas where Onchocerca volvulus and L. loa are co-endemic. In order to identify factors, including co-infections, which may explain the presence of high L. loa microfilaraemia in some individuals, we analysed data collected in 19 villages of central Cameroon. Two standardized skin snips and 30 mul of blood were obtained from each of 3190 participants and the microfilarial (mf) loads of both O. volvulus and L. loa were quantified. The data were analysed using multivariate hierarchical models. Individual-level variables were: age, sex, mf presence, and mf load; village-related variables included the endemicity levels for each infection. The two species show a certain degree of ecological separation in the study area. However, for a given individual host, the presence of microfilariae of one species was positively associated with the presence of microfilariae of the other (OR=1.79, 95% CI [1.43-2.24]). Among individuals harbouring Loa microfilariae, there was a slight positive relationship between the L. loa and O. volvulus mf loads which corresponded to an 11% increase in L. loa mf load per 100 O. volvulus microfilariae. Co-infection with O. volvulus is not sufficient to explain the very high L. loa mf loads harboured by some individuals
Local solutions in Sobolev spaces with negative indices for the "good" Boussinesq equation
We study the local well-posedness of the initial-value problem for the
nonlinear "good" Boussinesq equation with data in Sobolev spaces \textit{}
for negative indices of .Comment: Referee comments incorporate
A variational framework for flow optimization using semi-norm constraints
When considering a general system of equations describing the space-time
evolution (flow) of one or several variables, the problem of the optimization
over a finite period of time of a measure of the state variable at the final
time is a problem of great interest in many fields. Methods already exist in
order to solve this kind of optimization problem, but sometimes fail when the
constraint bounding the state vector at the initial time is not a norm, meaning
that some part of the state vector remains unbounded and might cause the
optimization procedure to diverge. In order to regularize this problem, we
propose a general method which extends the existing optimization framework in a
self-consistent manner. We first derive this framework extension, and then
apply it to a problem of interest. Our demonstration problem considers the
transient stability properties of a one-dimensional (in space) averaged
turbulent model with a space- and time-dependent model "turbulent viscosity".
We believe this work has a lot of potential applications in the fluid
dynamics domain for problems in which we want to control the influence of
separate components of the state vector in the optimization process.Comment: 30 page
Long-time dynamics of Rouse-Zimm polymers in dilute solutions with hydrodynamic memory
The dynamics of flexible polymers in dilute solutions is studied taking into
account the hydrodynamic memory, as a consequence of fluid inertia. As distinct
from the Rouse-Zimm (RZ) theory, the Boussinesq friction force acts on the
monomers (beads) instead of the Stokes force, and the motion of the solvent is
governed by the nonstationary Navier-Stokes equations. The obtained generalized
RZ equation is solved approximately. It is shown that the time correlation
functions describing the polymer motion essentially differ from those in the RZ
model. The mean-square displacement (MSD) of the polymer coil is at short times
\~ t^2 (instead of ~ t). At long times the MSD contains additional (to the
Einstein term) contributions, the leading of which is ~ t^(1/2). The relaxation
of the internal normal modes of the polymer differs from the traditional
exponential decay. It is displayed in the long-time tails of their correlation
functions, the longest-lived being ~ t^(-3/2) in the Rouse limit and t^(-5/2)
in the Zimm case, when the hydrodynamic interaction is strong. It is discussed
that the found peculiarities, in particular an effectively slower diffusion of
the polymer coil, should be observable in dynamic scattering experiments.Comment: 6 page
Commuting Flows and Conservation Laws for Noncommutative Lax Hierarchies
We discuss commuting flows and conservation laws for Lax hierarchies on
noncommutative spaces in the framework of the Sato theory. On commutative
spaces, the Sato theory has revealed essential aspects of the integrability for
wide class of soliton equations which are derived from the Lax hierarchies in
terms of pseudo-differential operators. Noncommutative extension of the Sato
theory has been already studied by the author and Kouichi Toda, and the
existence of various noncommutative Lax hierarchies are guaranteed. In the
present paper, we present conservation laws for the noncommutative Lax
hierarchies with both space-space and space-time noncommutativities and prove
the existence of infinite number of conserved densities. We also give the
explicit representations of them in terms of Lax operators. Our results include
noncommutative versions of KP, KdV, Boussinesq, coupled KdV, Sawada-Kotera,
modified KdV equations and so on.Comment: 22 pages, LaTeX, v2: typos corrected, references added, version to
appear in JM
Hamiltonian Structure, Symmetries and Conservation Laws for a Generalized (2 + 1)-Dimensional Double Dispersion Equation
This paper considers a generalized double dispersion equation depending on a nonlinear
function f (u) and four arbitrary parameters. This equation describes nonlinear dispersive waves in
2 + 1 dimensions and admits a Lagrangian formulation when it is expressed in terms of a potential
variable. In this case, the associated Hamiltonian structure is obtained. We classify all of the Lie
symmetries (point and contact) and present the corresponding symmetry transformation groups.
Finally, we derive the conservation laws from those symmetries that are variational, and we discuss
the physical meaning of the corresponding conserved quantities
A method to assess annual average renewable groundwater reserves for large regions in Spain
This paper proposes a method for assessing the groundwater renewable reserves of large regions for an average year, based on the integration of the recession curves for their basins springs or the natural base flow of their rivers. In this method, the hydrodynamic volume (or renewable reserves), were estimated from the baseflow equation. It was assumed that the flow was the same as the natural recharge, and that the recession coefficients were derived by the hydrogeological parameters and geometrical characteristics of aquifers, and adjusted to fit the recession curves at gauging stations. The method was applied to all the aquifers of Spain, which have a total groundwater renewable reserve of 86,895 hm3 four times the mean annual recharge. However, the distribution of these reserves is very variable; 18.6% of the country aquifers contain 94.7% of the entire reserve
Loa loa: More Than Meets the Eye?
Filarial nematodes cause neglected tropical diseases (NTDs) such as river blindness, elephantiasis, and African eye worm. Global control and elimination efforts are well underway for the former two, and epidemiological models have played a crucial role in understanding the impact of interventions and guiding control policy. However, for the latter (caused by Loa loa), there are no specific transmission models, and the disease has not been included among the prioritized NTDs. Maria-Gloria Basanez and her Helminth Ecology Research Group at Imperial College London work collaboratively on developing mathematical models for human and zoonotic helminthiases and other vector-borne NTDs. In this interview, the authors shared with Trends in Parasitology why loiasis may be more than meets the eye and how modelling can best be leveraged to help control human filarial infections
A double-layer Boussinesq-type model for highly nonlinear and dispersive waves
28 pages, 5 figures. Soumis à Proceedings of the Royal Society of London A.We derive and analyze in the framework of the mild-slope approximation a new double-layer Boussinesq-type model which is linearly and nonlinearly accurate up to deep water. Assuming the flow to be irrotational, we formulate the problem in terms of the velocity potential thereby lowering the number of unknowns. The model derivation combines two approaches, namely the method proposed by Agnon et al. (Agnon et al. 1999, J. Fluid Mech., 399 pp. 319-333) and enhanced by Madsen et al. (Madsen et al. 2003, Proc. R. Soc. Lond. A, 459 pp. 1075-1104) which consists in constructing infinite-series Taylor solutions to the Laplace equation, to truncate them at a finite order and to use Padé approximants, and the double-layer approach of Lynett & Liu (Lynett & Liu 2004, Proc. R. Soc. Lond. A, 460 pp. 2637-2669) allowing to lower the order of derivatives. We formulate the model in terms of a static Dirichlet-Neumann operator translated from the free surface to the still-water level, and we derive an approximate inverse of this operator that can be built once and for all. The final model consists of only four equations both in one and two horizontal dimensions, and includes only second-order derivatives, which is a major improvement in comparison with so-called high-order Boussinesq models. A linear analysis of the model is performed and its properties are optimized using a free parameter determining the position of the interface between the two layers. Excellent dispersion and shoaling properties are obtained, allowing the model to be applied up to deep water. Finally, numerical simulations are performed to quantify the nonlinear behaviour of the model, and the results exhibit a nonlinear range of validity reaching deep water areas
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