322 research outputs found
Therapie-induzierte Hyperinsulinämie: Wie kann man die unkontrollierte Insulindosiserhöhung vermeiden?
Cavitation inception of a van der Waals fluid at a sack-wall obstacle
Cavitation in a liquid moving past a constraint is numerically investigated
by means of a free-energy lattice Boltzmann simulation based on the van der
Waals equation of state. The fluid is streamed past an obstacle and, depending
on the pressure drop between inlet and outlet, vapor formation underneath the
corner of the sack-wall is observed. The circumstances of cavitation formation
are investigated and it is found that the local bulk pressure and mean stress
are insufficient to explain the phenomenon. Results obtained in this study
strongly suggest that the viscous stress, interfacial contributions to the
local pressure, and the Laplace pressure are relevant to the opening of a vapor
cavity. This can be described by a generalization of Joseph's criterion that
includes these contributions. A macroscopic investigation measuring mass flow
rate behavior and discharge coefficient was also performed. As theoretically
predicted, mass flow rate increases linearly with the square root of the
pressure drop. However, when cavitation occurs, the mass flow growth rate is
reduced and eventually it collapses into a choked flow state. In the cavitating
regime, as theoretically predicted and experimentally verified, the discharge
coefficient grows with the Nurick cavitation number
Generalized Gauge Theories and Weinberg-Salam Model with Dirac-K\"ahler Fermions
We extend previously proposed generalized gauge theory formulation of
Chern-Simons type and topological Yang-Mills type actions into Yang-Mills type
actions. We formulate gauge fields and Dirac-K\"ahler matter fermions by all
degrees of differential forms. The simplest version of the model which includes
only zero and one form gauge fields accommodated with the graded Lie algebra of
supergroup leads Weinberg-Salam model. Thus the Weinberg-Salam model
formulated by noncommutative geometry is a particular example of the present
formulation.Comment: 33 pages, LaTe
A wavelet based numerical method for nonlinear partial differential equations
The purpose of this paper is to present a wavelet–Galerkin scheme for solving
nonlinear elliptic partial differential equations. We select as trial spaces a nested
sequence of spaces from an appropriate biorthogonal multiscale analysis. This gives
rise to a nonlinear discretized system. To overcome the problems of nonlinearity, we
apply the machinery of interpolating wavelets to obtain knot oriented quadrature
rules. Finally, Newton’s method is applied to approximate the solution in the given
ansatz space. The results of some numerical experiments with different biorthogonal
systems, confirming the applicability of our scheme, are presented.Instituto de Cooperação Científica e Tecnológica Internacional - Acções Integradas Luso-Alemãs (DAAD/ICCTI) - Projecto DAAD/ICCTI nº 01141
Twisted Superspace for N=D=2 Super BF and Yang-Mills with Dirac-K\"ahler Fermion Mechanism
We propose a twisted D=N=2 superspace formalism. The relation between the
twisted super charges including the BRST charge, vector and pseudo scalar super
charges and the N=2 spinor super charges is established. We claim that this
relation is essentially related with the Dirac-K\"ahler fermion mechanism. We
show that a fermionic bilinear form of twisted N=2 chiral and anti-chiral
superfields is equivalent to the quantized version of BF theory with the Landau
type gauge fixing while a bosonic bilinear form leads to the N=2 Wess-Zumino
action. We then construct a Yang-Mills action described by the twisted N=2
chiral and vector superfields, and show that the action is equivalent to the
twisted version of the D=N=2 super Yang-Mills action, previously obtained from
the quantized generalized topological Yang-Mills action with instanton gauge
fixing.Comment: 36 page
Cholera hotspots and surveillance constraints contributing to recurrent epidemics in Tanzania
Objective: We described the dynamics of cholera in Tanzania between 2007 and 2017 and assessed the weaknesses of the current surveillance system in providing necessary data in achieving the global roadmap to 2030 for cholera control. Results: The Poisson-based spatial scan identifed cholera hotspots in mainland Tanzania. A zero-infated Poisson regression investigated the relationship between the incidence of cholera and available demographic, socio-economic and climatic exposure variables. Four cholera hotspots were detected covering 17 regions, home to 28 million people, including the central regions and those surrounding the Lakes Victoria, Tanganyika and Nyaza. The risk of experiencing cholera in these regions was up to 2.9 times higher than elsewhere in the country. Regression analyses revealed that every 100 km of water perimeter in a region increased the cholera incidence by 1.5%. Due to the compilation of surveillance data at regional level rather than at district, we were unable to reliably identify any other signifcant risk factors and specifc hotspots. Cholera high-risk populations in Tanzania include those living near lakes and central regions. Successful surveillance require disaggregated data available weekly and at district levels in order to serve as data for action to support the roadmap for cholera control.Published versio
Characterizing the turbulent drag properties of rough surfaces with a Taylor--Couette setup
Wall-roughness induces extra drag in wall-bounded turbulent flows. Mapping
any given roughness geometry to its fluid dynamic behaviour has been hampered
by the lack of accurate and direct measurements of skin-friction drag. Here the
Taylor-Couette (TC) system provides an opportunity as it is a closed system and
allows to directly and reliably measure the skin-friction. However, the
wall-curvature potentially complicates the connection between the wall friction
and the wall roughness characteristics. Here we investigate the effects of a
hydrodynamically fully rough surface on highly turbulent, inner cylinder
rotating, TC flow. We find that the effects of a hydrodynamically fully rough
surface on TC turbulence, where the roughness height k is three orders of
magnitude smaller than the Obukhov curvature length Lc (which characterizes the
effects of curvature on the turbulent flow, see Berghout et al. arXiv:
2003.03294, 2020), are similar to those effects of a fully rough surface on a
flat plate turbulent boundary layer (BL). Hence, the value of the equivalent
sand grain height ks, that characterizes the drag properties of a rough
surface, is similar to those found for comparable sandpaper surfaces in a flat
plate BL. Next, we obtain the dependence of the torque (skin-friction drag) on
the Reynolds number for given wall roughness, characterized by ks, and find
agreement with the experimental results within 5 percent. Our findings
demonstrate that global torque measurements in the TC facility are well suited
to reliably deduce wall drag properties for any rough surface.Comment: 18 pages, 13 figure
Positivity and conservation of superenergy tensors
Two essential properties of energy-momentum tensors T_{\mu\nu} are their
positivity and conservation. This is mathematically formalized by,
respectively, an energy condition, as the dominant energy condition, and the
vanishing of their divergence \nabla^\mu T_{\mu\nu}=0. The classical Bel and
Bel-Robinson superenergy tensors, generated from the Riemann and Weyl tensors,
respectively, are rank-4 tensors. But they share these two properties with
energy momentum tensors: the Dominant Property (DP) and the divergence-free
property in the absence of sources (vacuum). Senovilla defined a universal
algebraic construction which generates a basic superenergy tensor T{A} from any
arbitrary tensor A. In this construction the seed tensor A is structured as an
r-fold multivector, which can always be done. The most important feature of the
basic superenergy tensors is that they satisfy automatically the DP,
independently of the generating tensor A. In a previous paper we presented a
more compact definition of T{A} using the r-fold Clifford algebra. This form
for the superenergy tensors allowed to obtain an easy proof of the DP valid for
any dimension. In this paper we include this proof. We explain which new
elements appear when we consider the tensor T{A} generated by a
non-degree-defined r-fold multivector A and how orthogonal Lorentz
transformations and bilinear observables of spinor fields are included as
particular cases of superenergy tensors. We find some sufficient conditions for
the seed tensor A, which guarantee that the generated tensor T{A} is
divergence-free. These sufficient conditions are satisfied by some physical
fields, which are presented as examples.Comment: 19 pages, no figures. Language and minor changes. Published versio
New Results in Sasaki-Einstein Geometry
This article is a summary of some of the author's work on Sasaki-Einstein
geometry. A rather general conjecture in string theory known as the AdS/CFT
correspondence relates Sasaki-Einstein geometry, in low dimensions, to
superconformal field theory; properties of the latter are therefore reflected
in the former, and vice versa. Despite this physical motivation, many recent
results are of independent geometrical interest, and are described here in
purely mathematical terms: explicit constructions of infinite families of both
quasi-regular and irregular Sasaki-Einstein metrics; toric Sasakian geometry;
an extremal problem that determines the Reeb vector field for, and hence also
the volume of, a Sasaki-Einstein manifold; and finally, obstructions to the
existence of Sasaki-Einstein metrics. Some of these results also provide new
insights into Kahler geometry, and in particular new obstructions to the
existence of Kahler-Einstein metrics on Fano orbifolds.Comment: 31 pages, no figures. Invited contribution to the proceedings of the
conference "Riemannian Topology: Geometric Structures on Manifolds"; minor
typos corrected, reference added; published version; Riemannian Topology and
Geometric Structures on Manifolds (Progress in Mathematics), Birkhauser (Nov
2008
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