505,934 research outputs found
Reactions at surfaces studied by ab initio dynamics calculations
Due to the development of efficient algorithms and the improvement of
computer power it is now possible to map out potential energy surfaces (PES) of
reactions at surfaces in great detail. This achievement has been accompanied by
an increased effort in the dynamical simulation of processes on surfaces. The
paradigm for simple reactions at surfaces -- the dissociation of hydrogen on
metal surfaces -- can now be treated fully quantum dynamically in the molecular
degrees of freedom from first principles, i.e., without invoking any adjustable
parameters. This relatively new field of ab initio dynamics simulations of
reactions at surfaces will be reviewed. Mainly the dissociation of hydrogen on
clean and adsorbate covered metal surfaces and on semiconductor surfaces will
be discussed. In addition, the ab initio molecular dynamics treatment of
reactions of hydrogen atoms with hydrogen-passivated semiconductor surfaces and
recent achievements in the ab initio description of laser-induced desorption
and further developments will be addressed.Comment: 33 pages, 19 figures, submitted to Surf. Sci. Rep. Other related
publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm
Regularity properties of nonlocal minimal surfaces via limiting arguments
We prove an improvement of flatness result for nonlocal minimal surfaces
which is independent of the fractional parameter when .
As a consequence, we obtain that all the nonlocal minimal cones are flat and
that all the nonlocal minimal surfaces are smooth when the dimension of the
ambient space is less or equal than 7 and is close to 1
On rational maps from a general surface in P^3 to surfaces of general type
We study the dominant rational maps from a general surface in P^{3} to
surfaces of general type. We prove restrictions on the target surfaces, and
special properties of the rational maps. We show that for a small degree the
general surface has no such map. Moreover a slight improvement of a result of
Catanese, on the number of moduli of a surface of general type, is also
obtained.Comment: 19 pages, accepted in Advances in Geometr
Topology of modified helical gears
The topology of several types of modified surfaces of helical gears is proposed. The modified surfaces allow absorption of a linear or almost linear function of transmission errors. These errors are caused by gear misalignment and an improvement of the contact of gear tooth surfaces. Principles and corresponding programs for computer aided simulation of meshing and contact of gears have been developed. The results of this investigation are illustrated with numerical examples
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
The Invariant Measures of some Infinite Interval Exchange Maps
We classify the locally finite ergodic invariant measures of certain infinite
interval exchange transformations (IETs). These transformations naturally arise
from return maps of the straight-line flow on certain translation surfaces, and
the study of the invariant measures for these IETs is equivalent to the study
of invariant measures for the straight-line flow in some direction on these
translation surfaces. For the surfaces and directions for which our methods
apply, we can characterize the locally finite ergodic invariant measures of the
straight-line flow in a set of directions of Hausdorff dimension larger than
1/2. We promote this characterization to a classification in some cases. For
instance, when the surfaces admit a cocompact action by a nilpotent group, we
prove each ergodic invariant measure for the straight-line flow is a Maharam
measure, and we describe precisely which Maharam measures arise. When the
surfaces under consideration are finite area, the straight-line flows in the
directions we understand are uniquely ergodic. Our methods apply to translation
surfaces admitting multi-twists in a pair of cylinder decompositions in
non-parallel directions.Comment: 107 pages, 11 figures. Minor improvement
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