92,357 research outputs found
The topographic development and areal parametric characterization of a stratified surface polished by mass finishing
Mass finishing is amongst the most widely used finishing processes in modern manufacturing, in applications from deburring to edge radiusing and polishing. Processing objectives are varied, ranging from the cosmetic to the functionally critical. One such critical application is the hydraulically smooth polishing of aero engine component gas-washed surfaces. In this, and many other applications the drive to improve process control and finish tolerance is ever present. Considering its widespread use mass finishing has seen limited research activity, particularly with respect to surface characterization. The objectives of the current paper are to; characterise the mass finished stratified surface and its development process using areal surface parameters, provide guidance on the optimal parameters and sampling method to characterise this surface type for a given application, and detail the spatial variation in surface topography due to coupon edge shadowing. Blasted and peened square plate coupons in titanium alloy are wet (vibro) mass finished iteratively with increasing duration. Measurement fields are precisely relocated between iterations by fixturing and an image superimposition alignment technique. Surface topography development is detailed with ālog of process durationā plots of the āareal parameters for scale-limited stratified functional surfacesā, (the Sk family). Characteristic features of the Smr2 plot are seen to map out the processing of peak, core and dale regions in turn. These surface process regions also become apparent in the ālog of process durationā plot for Sq, where lower core and dale regions are well modelled by logarithmic functions. Surface finish (Ra or Sa) with mass finishing duration is currently predicted with an exponential model. This model is shown to be limited for the current surface type at a critical range of surface finishes.
Statistical analysis provides a group of areal parameters including; Vvc, Sq, and Sdq, showing optimal discrimination for a specific range of surface finish outcomes. As a consequence of edge shadowing surface segregation is suggested for characterization purposes
On certain diophantine equations of diagonal type
In this note we consider Diophantine equations of the form \begin{equation*}
a(x^p-y^q) = b(z^r-w^s), \quad \mbox{where}\quad
\frac{1}{p}+\frac{1}{q}+\frac{1}{r}+\frac{1}{s}=1, \end{equation*} with even
positive integers . We show that in each case the set of rational
points on the underlying surface is dense in the Zariski topology. For the
surface with we prove density of rational points in the
Euclidean topology. Moreover, in this case we construct infinitely many
parametric solutions in coprime polynomials. The same result is true for
. In the case , we
present some new parametric solutions of the equation .Comment: 16 pages, revised version will appear in the Journal of Number Theor
Oka manifolds: From Oka to Stein and back
Oka theory has its roots in the classical Oka-Grauert principle whose main
result is Grauert's classification of principal holomorphic fiber bundles over
Stein spaces. Modern Oka theory concerns holomorphic maps from Stein manifolds
and Stein spaces to Oka manifolds. It has emerged as a subfield of complex
geometry in its own right since the appearance of a seminal paper of M. Gromov
in 1989.
In this expository paper we discuss Oka manifolds and Oka maps. We describe
equivalent characterizations of Oka manifolds, the functorial properties of
this class, and geometric sufficient conditions for being Oka, the most
important of which is Gromov's ellipticity. We survey the current status of the
theory in terms of known examples of Oka manifolds, mention open problems and
outline the proofs of the main results.
In the appendix by F. Larusson it is explained how Oka manifolds and Oka
maps, along with Stein manifolds, fit into an abstract homotopy-theoretic
framework.
The article is an expanded version of the lectures given by the author at the
Winter School KAWA-4 in Toulouse, France, in January 2013. A more comprehensive
exposition of Oka theory is available in the monograph F. Forstneric, Stein
Manifolds and Holomorphic Mappings (The Homotopy Principle in Complex
Analysis), Ergebnisse der Mathematik und ihrer Grenzgebiete, 3. Folge, 56,
Springer-Verlag, Berlin-Heidelberg (2011).Comment: With an appendix by Finnur Larusson. To appear in Ann. Fac. Sci.
Toulouse Math. (6), vol. 22, no. 4. This version is identical with the
published tex
Human hepatic cell behavior on polysulfone membrane with double porosity level
In the membrane-based bioartificial livers developed up to now,the hepatic cells were located either in the fibers lumen or in the cartridge,with limited capacity for cell hosting.Here,we designed a polysulfone (PSU) membrane with a double porosity level:(i)surface macroporosity emerging in
macrochambers accessible to hepatic cell colonization;(ii)microporosity to ensure gas and molecule transfers between macrochambers and supernatant,as well as potential immune barrier. ESEM and X-ray tomography confirmed that macrochambers accessed the membrane surface and were inter-connected. Biocompatibility and performances of this PSU membrane with double porosity level were compared to classical semi-permeable structures,following cell organization,cell proliferation and liver specific activities over a 9 days incubation. Macrochambers were colonized by hepatic cells, leading to higher albumin synthesis compared to control.Therefore,this membrane with double porosity appeared as a promising support to offer an inner 3D environment adequate to cell proliferation to form a liver-like tissue
A survey of partial differential equations in geometric design
YesComputer aided geometric design is an area
where the improvement of surface generation techniques
is an everlasting demand since faster and more accurate
geometric models are required. Traditional methods
for generating surfaces were initially mainly based
upon interpolation algorithms. Recently, partial differential
equations (PDE) were introduced as a valuable
tool for geometric modelling since they offer a number
of features from which these areas can benefit. This work
summarises the uses given to PDE surfaces as a surface
generation technique togethe
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