3,130 research outputs found
Combining gravity with the forces of the standard model on a cosmological scale
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the underlying spacetime is a Friedman universe with flat spatial
slices and where the matter fields are comprised of the strong interaction,
with \SU(3) replaced by a general \SU(n), , and the electro-weak
interaction. The wave functions are maps from to a subspace of the
antisymmetric Fock space, and one noteworthy result is that, whenever the
electro-weak interaction is involved, the image of an eigenfunction is in
general not one dimensional, i.e., in general it makes no sense specifying a
fermion and looking for an eigenfunction the range of which is contained in the
one dimensional vector space spanned by the fermion.Comment: 53 pages, v6: some typos correcte
Expansion of pinched hypersurfaces of the Euclidean and hyperbolic space by high powers of curvature
We prove convergence results for expanding curvature flows in the Euclidean
and hyperbolic space. The flow speeds have the form , where and
is a positive, strictly monotone and 1-homogeneous curvature function. In
particular this class includes the mean curvature . We prove that a
certain initial pinching condition is preserved and the properly rescaled
hypersurfaces converge smoothly to the unit sphere. We show that an example due
to Andrews-McCoy-Zheng can be used to construct strictly convex initial
hypersurfaces, for which the inverse mean curvature flow to the power
loses convexity, justifying the necessity to impose a certain pinching
condition on the initial hypersurface.Comment: 18 pages. We included an example for the loss of convexity and
pinching. In the third version we dropped the concavity assumption on F.
Comments are welcom
Quantum cosmological Friedman models with a massive Yang-Mills field
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the matter field is provided by a massive Yang-Mills field. The
resolution is achieved by first solving the free eigenvalue problem for the
gravitational field and then the constrained eigenvalue problem for the
Yang-Mills field. In the latter case the mass of the Yang-Mills field assumes
the role of the eigenvalue.Comment: 16 pages, v3: typos corrected, final version, to appear in CQ
Tribology of Skin: Review and Analysis of Experimental Results for the Friction Coefficient of Human Skin
In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin friction coefficients. Starting with an overview on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing experimental data and compare the results for different anatomical skin areas and friction measurement techniques. For this purpose, we also estimated and analysed skin contact pressures applied during the various friction measurements. The detailed analyses show that substantial variations are a characteristic feature of friction coefficients measured for skin and that differences in skin hydration are the main cause thereof, followed by the influences of surface and material properties of the contacting materials. When the friction coefficients of skin are plotted as a function of the contact pressure, the majority of the literature data scatter over a wide range that can be explained by the adhesion friction model. The case of dry skin is reflected by relatively low and pressure-independent friction coefficients (greater than 0.2 and typically around 0.5), comparable to the dry friction of solids with rough surfaces. In contrast, the case of moist or wet skin is characterised by significantly higher (typically >1) friction coefficients that increase strongly with decreasing contact pressure and are essentially determined by the mechanical shear properties of wet skin. In several studies, effects of skin deformation mechanisms contributing to the total friction are evident from friction coefficients increasing with contact pressure. However, the corresponding friction coefficients still lie within the range delimited by the adhesion friction model. Further research effort towards the analysis of the microscopic contact area and mechanical properties of the upper skin layers is needed to improve our so far limited understanding of the complex tribological behaviour of human ski
Intrinsic time gravity and the Lichnerowicz-York equation
We investigate the effect on the Hamiltonian structure of general relativity
of choosing an intrinsic time to fix the time slicing. 3-covariance with
momentum constraint is maintained, but the Hamiltonian constraint is replaced
by a dynamical equation for the trace of the momentum. This reveals a very
simple structure with a local reduced Hamiltonian. The theory is easily
generalised; in particular, the square of the Cotton-York tensor density can be
added as an extra part of the potential while at the same time maintaining the
classic 2 + 2 degrees of freedom. Initial data construction is simple in the
extended theory; we get a generalised Lichnerowicz-York equation with nice
existence and uniqueness properties. Adding standard matter fields is quite
straightforward.Comment: 4 page
Fabrication, Characterisation and Tribological Investigation of Artificial Skin Surface Lipid Films
This article deals with the tribology of lipid coatings that resemble those found on human skin. In order to simulate the lipidic surface chemistry of human skin, an artificial sebum formulation that closely resembles human sebum was spray-coated onto mechanical skin models in physiologically relevant concentrations (5-100μg/cm2). Water contact angles and surface free energies (SFEs) showed that model surfaces with ≤25μg/cm2 lipids appropriately mimic the physico-chemical properties of dry, sebum-poor skin regions. In friction experiments with a steel ball, lipid-coated model surfaces demonstrated lubrication effects over a wide range of sliding velocities and normal loads. In friction measurements on model surfaces as a function of lipid-film thickness, a clear minimum in the friction coefficient (COF) was observed in the case of hydrophilic, high-SFE materials (steel, glass), with the lowest COF (≈0.5) against skin model surfaces being found at 25μg/cm2 lipids. For hydrophobic, low-SFE polymers, the COF was considerably lower (0.4 for PP, 0.16 for PTFE) and relatively independent of the lipid amount, indicating that both the mechanical and surface-chemical properties of the sliders strongly influence the friction behaviour of the skin-model surfaces. Lipid-coated skin models might be a valuable tool not only for tribologists but also for cosmetic chemists, in that they allow the objective study of friction, adhesion and wetting behaviour of liquids and emulsions on simulated skin-surface condition
Identificação e clonagem de promotores raiz-especÃficos de eucalipto.
A utilização de promotores tecido - especÃficos é uma das principais estratégias para direcionar a expres são de transgenes a determinados órgãos ou tipos celulares . Por isso, o objetivo deste trabalho foi a clonagem de promotores raiz - especÃficos , a partir de dados de RNA - Seq obtidos de bibliotecas de raiz, xilema e folha de eucalipto. Dois genes com padrão d e expressão preferencial em raiz foram inicialmente selecionados para isolamento da região promotora. Fragmentos de 1kb foram clonados em vetor binário pCAMBIA2301, fusionados ao gene repórter da beta - glucuronidase (GUS) , para transformação de Populus trem ula x Populus alba via Agrobacterium tumefaciens .Edição dos anais do 3º Simpósio de BioquÃmica e Biotecnologia, 2013. Londrina
The prescribed mean curvature equation in weakly regular domains
We show that the characterization of existence and uniqueness up to vertical
translations of solutions to the prescribed mean curvature equation, originally
proved by Giusti in the smooth case, holds true for domains satisfying very
mild regularity assumptions. Our results apply in particular to the
non-parametric solutions of the capillary problem for perfectly wetting fluids
in zero gravity. Among the essential tools used in the proofs, we mention a
\textit{generalized Gauss-Green theorem} based on the construction of the weak
normal trace of a vector field with bounded divergence, in the spirit of
classical results due to Anzellotti, and a \textit{weak Young's law} for
-minimizers of the perimeter.Comment: 23 pages, 1 figure --- The results on the weak normal trace of vector
fields have been now extended and moved in a self-contained paper available
at: arXiv:1708.0139
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