1,267 research outputs found
The Dynamics of Public Goods
We analyze the replicator equation for two games closely related with the social dilemma occurring in public goods situation. In one case, players can punish defectors in their group. In another case, they can choose not to take part in the game. In both cases, interactions are not pairwise and payoffs are nonlinear. Nevertheless, the qualitative dynamics can be fully analyzed. The games offer potential solutions for the problem of the emergence of cooperation in sizeable groups of non-related individuals - a basic question in evolutionary biology and economics
Fundamental limitations to gain enhancement in periodic media and waveguides
A common strategy to compensate for losses in optical nanostructures is to
add gain material in the system. By exploiting slow-light effects it is
expected that the gain may be enhanced beyond its bulk value. Here we show that
this route cannot be followed uncritically: inclusion of gain inevitably
modifies the underlying dispersion law, and thereby may degrade the slow-light
properties underlying the device operation and the anticipated gain enhancement
itself. This degradation is generic; we demonstrate it for three different
systems of current interest (coupled resonator optical waveguides, Bragg
stacks, and photonic crystal waveguides). Nevertheless, a small amount of added
gain may be beneficial
On the competition for ultimately stiff and strong architected materials
Advances in manufacturing techniques may now realize virtually any imaginable
microstructures, paving the way for architected materials with properties
beyond those found in nature. This has lead to a quest for closing gaps in
property-space by carefully designed metamaterials. Development of mechanical
metamaterials has gone from open truss lattice structures to closed plate
lattice structures with stiffness close to theoretical bounds. However, the
quest for optimally stiff and strong materials is complex. Plate lattice
structures have higher stiffness and (yield) strength but are prone to buckling
at low volume fractions. Hence here, truss lattice structures may still be
optimal. To make things more complicated, hollow trusses or structural
hierarchy bring closed-walled microstructures back in the competition. Based on
analytical and numerical studies of common microstructures from the literature,
we provide higher order interpolation schemes for their effective stiffness and
(buckling) strength. Furthermore, we provide a case study based on
multi-property Ashby charts for weight-optimal porous beams under bending, that
demonstrates the intricate interplay between structure and microarchitecture
that plays the key role in the design of ultimate load carrying structures. The
provided interpolation schemes may also be used to account for microstructural
yield and buckling in multiscale design optimization schemes.Comment: 18 pages main manuscript with 6 figures and 10 pages appendix with 2
figure
Topology Optimization and 3D printing of Large Deformation Compliant Mechanisms for Straining Biological Tissues
This paper presents a synthesis approach in a density-based topology
optimization setting to design large deformation compliant mechanisms for
inducing desired strains in biological tissues. The modelling is based on
geometrical nonlinearity together with a suitably chosen hypereleastic material
model, wherein the mechanical equilibrium equations are solved using the total
Lagrangian finite element formulation. An objective based on least-square error
with respect to target strains is formulated and minimized with the given set
of constraints and the appropriate surroundings of the tissues. To circumvent
numerical instabilities arising due to large deformation in low stiffness
design regions during topology optimization, a strain-energy based
interpolation scheme is employed. The approach uses an extended robust
formulation i.e. the eroded, intermediate and dilated projections for the
design description as well as variation in tissue stiffness. Efficacy of the
synthesis approach is demonstrated by designing various compliant mechanisms
for providing different target strains in biological tissue constructs.
Optimized compliant mechanisms are 3D-printed and their performances are
recorded in a simplified experiment and compared with simulation results
obtained by a commercial software.Comment: 23 pages, 14 figure
Duplication-divergence model of protein interaction network
We show that the protein-protein interaction networks can be surprisingly
well described by a very simple evolution model of duplication and divergence.
The model exhibits a remarkably rich behavior depending on a single parameter,
the probability to retain a duplicated link during divergence. When this
parameter is large, the network growth is not self-averaging and an average
vertex degree increases algebraically. The lack of self-averaging results in a
great diversity of networks grown out of the same initial condition. For small
values of the link retention probability, the growth is self-averaging, the
average degree increases very slowly or tends to a constant, and a degree
distribution has a power-law tail.Comment: 8 pages, 13 figure
The decontamination of radioactive ion exchange resins using neutral salts as elutriants
Includes bibliographical references (leaves 124-126
Dissipative Landau-Zener transitions of a qubit: bath-specific and universal behavior
We study Landau-Zener transitions in a qubit coupled to a bath at zero
temperature. A general formula is derived that is applicable to models with a
non-degenerate ground state. We calculate exact transition probabilities for a
qubit coupled to either a bosonic or a spin bath. The nature of the baths and
the qubit-bath coupling is reflected in the transition probabilities. For
diagonal coupling, when the bath causes energy fluctuations of the diabatic
qubit states but no transitions between them, the transition probability
coincides with the standard LZ probability of an isolated qubit. This result is
universal as it does not depend on the specific type of bath. For pure
off-diagonal coupling, by contrast, the tunneling probability is sensitive to
the coupling strength. We discuss the relevance of our results for experiments
on molecular nanomagnets, in circuit QED, and for the fast-pulse readout of
superconducting phase qubits.Comment: 16 pages, 8 figure
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