12,846 research outputs found
Multi-field modelling and simulation of large deformation ductile fracture
In the present contribution we focus on a phase-field approach to ductile fracture applied to large deformation contact problems. Phase-field approaches to fracture allow for an efficient numerical investigation of complex three-dimensional fracture problems, as they arise in contact and impact situations. To account for large deformations the underlying formulation is based on a multiplicative decomposition of the deformation gradient into an elastic and plastic part. Moreover, we make use of a fourth-order crack regularization combined with gradient plasticity. Eventually, a demonstrative example shows the capability of the proposed framework
An approach to metal fatigue
Cumulative fatigue damage based on investigation of fatigue limit associated with crack, crack propagation rate, and stress interaction cycle in metal
Optimal control of circuit quantum electrodynamics in one and two dimensions
Optimal control can be used to significantly improve multi-qubit gates in
quantum information processing hardware architectures based on superconducting
circuit quantum electrodynamics. We apply this approach not only to dispersive
gates of two qubits inside a cavity, but, more generally, to architectures
based on two-dimensional arrays of cavities and qubits. For high-fidelity gate
operations, simultaneous evolutions of controls and couplings in the two
coupling dimensions of cavity grids are shown to be significantly faster than
conventional sequential implementations. Even under experimentally realistic
conditions speedups by a factor of three can be gained. The methods immediately
scale to large grids and indirect gates between arbitrary pairs of qubits on
the grid. They are anticipated to be paradigmatic for 2D arrays and lattices of
controllable qubits.Comment: Published version
Ignition points and combustion reactions in Diesel engines. Part II
Ignition point measurement and ignition point test equipment is examined
Determination of ignition points of liquid fuels under pressure
Two series of experiments were tried, in order to determine the ignition point at any desired pressure, the first series at constant and the second at varying pressure. The results differ greatly and indicate that testing under pressure, in the investigation of liquid fuels, can be done best in the laboratory and that the determination of the ignition points in an open vessel furnishes no certain indication of the behavior of the fuel in the engine
Ignition points and combustion reactions in Diesel engines. Part I
The question of whether the fuel should be adapted to the engine or whether it is possible to improve equipment such as carburetors and engines so that as much of the crude oil as possible may be used without further transformation is examined in this report. Various ignition points and fuel mixtures are investigated in this regard
Regular Incidence Complexes, Polytopes, and C-Groups
Regular incidence complexes are combinatorial incidence structures
generalizing regular convex polytopes, regular complex polytopes, various types
of incidence geometries, and many other highly symmetric objects. The special
case of abstract regular polytopes has been well-studied. The paper describes
the combinatorial structure of a regular incidence complex in terms of a system
of distinguished generating subgroups of its automorphism group or a
flag-transitive subgroup. Then the groups admitting a flag-transitive action on
an incidence complex are characterized as generalized string C-groups. Further,
extensions of regular incidence complexes are studied, and certain incidence
complexes particularly close to abstract polytopes, called abstract polytope
complexes, are investigated.Comment: 24 pages; to appear in "Discrete Geometry and Symmetry", M. Conder,
A. Deza, and A. Ivic Weiss (eds), Springe
Automatically Discovering Hidden Transformation Chaining Constraints
Model transformations operate on models conforming to precisely defined
metamodels. Consequently, it often seems relatively easy to chain them: the
output of a transformation may be given as input to a second one if metamodels
match. However, this simple rule has some obvious limitations. For instance, a
transformation may only use a subset of a metamodel. Therefore, chaining
transformations appropriately requires more information. We present here an
approach that automatically discovers more detailed information about actual
chaining constraints by statically analyzing transformations. The objective is
to provide developers who decide to chain transformations with more data on
which to base their choices. This approach has been successfully applied to the
case of a library of endogenous transformations. They all have the same source
and target metamodel but have some hidden chaining constraints. In such a case,
the simple metamodel matching rule given above does not provide any useful
information
The Star Formation History of NGC 1705: a Post-Starburst Galaxy on the Verge of Activity
We infer the star formation history in different regions of the blue compact
dwarf NGC 1705 by comparing synthetic color-magnitude diagrams with HST optical
and near-infrared photometry. We find that NGC 1705 is not a young galaxy
because its star formation commenced at least 5 Gyr ago. On the other hand, we
confirm the existence of a recent burst of star formation between 15 and 10 Myr
ago. We also find evidence for new strong activity, which started 3 Myr ago and
is still continuing. The old population is spread across the entire galaxy,
while the young and intermediate stars are more concentrated in the central
regions. We derive an almost continuous star formation with variable rate, and
exclude the presence of long quiescent phases between the episodes during the
last ~1 Gyr. The central regions experienced an episode of star formation of
\~0.07 Msun/yr (for a Salpeter initial mass function [IMF]) 15 to 10 Myr ago.
This coincides with the strong activity in the central super star cluster. We
find a rate of ~0.3 Msun/yr for the youngest ongoing burst which started ~3 Myr
ago. This is higher than in other dwarfs and comparable to the rate of NGC
1569. The star formation rate of earlier episodes is not especially high and
falls in the range 10^{-3}-10^{-1} Msun/yr. The IMF is close to the Salpeter
value or slightly steeper.Comment: 34 pages, including 6 tables and 14 .ps figures (9 in colour), AJ in
pres
- …