1,103 research outputs found
A Potts Neuron Approach to Communication Routing
A feedback neural network approach to communication routing problems is
developed with emphasis on Multiple Shortest Path problems, with several
requests for transmissions between distinct start- and endnodes. The basic
ingredients are a set of Potts neurons for each request, with interactions
designed to minimize path lengths and to prevent overloading of network arcs.
The topological nature of the problem is conveniently handled using a
propagator matrix approach. Although the constraints are global, the
algorithmic steps are based entirely on local information, facilitating
distributed implementations. In the polynomially solvable single-request case
the approach reduces to a fuzzy version of the Bellman-Ford algorithm. The
approach is evaluated for synthetic problems of varying sizes and load levels,
by comparing with exact solutions from a branch-and-bound method. With very few
exceptions, the Potts approach gives legal solutions of very high quality. The
computational demand scales merely as the product of the numbers of requests,
nodes, and arcs.Comment: 10 pages LaTe
Scaling and Scale Breaking in Polyelectrolyte
We consider the thermodynamics of a uniformly charged polyelectrolyte with
harmonic bonds. For such a system there is at high temperatures an approximate
scaling of global properties like the end-to-end distance and the interaction
energy with the chain-length divided by the temperature. This scaling is broken
at low temperatures by the ultraviolet divergence of the Coulomb potential. By
introducing a renormalization of the strength of the nearest- neighbour
interaction the scaling is restored, making possible an efficient blocking
method for emulating very large polyelectrolytes using small systems. The high
temperature behaviour is well reproduced by the analytical high- expansions
even for fairly low temperatures and system sizes. In addition, results from
low- expansions, where the coefficients have been computed numerically, are
presented. These results approximate well the corresponding Monte Carlo results
at realistic temperatures. A corresponding analysis of screened chains is
performed. The situation here is complicated by the appearance of an additional
parameter, the screening length. A window is found in parameter space, where
scaling holds for the end-to-end distance. This window corresponds to
situations where the range of the potential interpolates between the bond
length and the size of the chain. This scaling behaviour, which is verified by
Monte Carlo results, is consistent with Flory scaling. Also for the screened
chain a blocking approach can be devised, that performs well for low
temperatures, whereas the low- expansion is inaccurate at realistic
temperatures.Comment: 18 pages, latex, 6 figure
Properties of Random Graphs with Hidden Color
We investigate in some detail a recently suggested general class of ensembles
of sparse undirected random graphs based on a hidden stub-coloring, with or
without the restriction to nondegenerate graphs. The calculability of local and
global structural properties of graphs from the resulting ensembles is
demonstrated. Cluster size statistics are derived with generating function
techniques, yielding a well-defined percolation threshold. Explicit rules are
derived for the enumeration of small subgraphs. Duality and redundancy is
discussed, and subclasses corresponding to commonly studied models are
identified.Comment: 14 pages, LaTeX, no figure
The Electrostatic Persistence Length Calculated from Monte Carlo, Variational and Perturbation Methods
Monte Carlo simulations and variational calculations using a Gaussian ansatz
are applied to a model consisting of a flexible linear polyelectrolyte chain as
well as to an intrinsically stiff chain with up to 1000 charged monomers.
Addition of salt is treated implicitly through a screened Coulomb potential for
the electrostatic interactions.
For the flexible model the electrostatic persistence length shows roughly
three regimes in its dependence on the Debye-H\"{u}ckel screening length,
.As long as the salt content is low and is longer
than the end-to-end distance, the electrostatic persistence length varies only
slowly with . Decreasing the screening length, a controversial
region is entered. We find that the electrostatic persistence length scales as
, in agreement with experiment on flexible
polyelectrolytes, where is a strength parameter measuring the
electrostatic interactions within the polyelectrolyte. For screening lengths
much shorter than the bond length, the dependence becomes
quadratic in the variational calculation. The simulations suffer from numerical
problems in this regime, but seem to give a relationship half-way between
linear and quadratic.
A low temperature expansion only reproduces the first regime and a high
temperature expansion, which treats the electrostatic interactions as a
perturbation to a Gaussian chain, gives a quadratic dependence on the Debye
length.
For a sufficiently stiff chain, the persistence length varies quadratically
with in agreement with earlier theories.Comment: 20 pages LaTeX, 9 postscript figure
The causal impact of economic growth on material use in Europe
Several scholars and policy-makers have claimed that Europe, and Western Europe in particular, has managed to âdecoupleâ economic growth from material use. We identify and address one major limitation in the existing literature â failure to take the endogeneity of economic growth into account. Based on a panel data-set of 32 European countries from 2000 to 2014, we estimate the causal impact of gross domestic product (GDP) on domestic material consumption (DMC) applying an instrumental variable approach. We use the number of storm occurrences as an instrument for GDP, which we show is both relevant and valid. Our results provide new evidence that increasing the GDP growth rate causes the DMC growth rate to increase for Western Europe, whereas the effect is insignificant for the Eastern European economies and Europe as a whole. As our results partly question current wisdom on the achievements of âdecouplingâ, especially among European policy-makers, we offer two explanations that are consistent with these results
Analysis of complex contagions in random multiplex networks
We study the diffusion of influence in random multiplex networks where links
can be of different types, and for a given content (e.g., rumor, product,
political view), each link type is associated with a content dependent
parameter in that measures the relative bias type- links
have in spreading this content. In this setting, we propose a linear threshold
model of contagion where nodes switch state if their "perceived" proportion of
active neighbors exceeds a threshold \tau. Namely, a node connected to
active neighbors and inactive neighbors via type- links will turn
active if exceeds its threshold \tau. Under this
model, we obtain the condition, probability and expected size of global
spreading events. Our results extend the existing work on complex contagions in
several directions by i) providing solutions for coupled random networks whose
vertices are neither identical nor disjoint, (ii) highlighting the effect of
content on the dynamics of complex contagions, and (iii) showing that
content-dependent propagation over a multiplex network leads to a subtle
relation between the giant vulnerable component of the graph and the global
cascade condition that is not seen in the existing models in the literature.Comment: Revised 06/08/12. 11 Pages, 3 figure
Phase diagram of Fe-doped Ni-Mn-Ga ferromagnetic shape-memory alloys
We have studied the effect of Fe addition on the structural and magnetic
transitions in the magnetic shape memory alloy Ni-Mn-Ga by substituting
systematically each atomic species by Fe. Calorimetric and AC susceptibility
measurements have been carried out in order to study the magnetic and
structural transformation properties. We find that the addition of Fe modifies
the structural and magnetic transformation temperatures. Magnetic transition
temperatures are displaced to higher values when Fe is substituted into
Ni-Mn-Ga, while martensitic and premartensitic transformation temperatures
shift to lower values. Moreover, it has been found that the electron per atom
concentration essentially governs the phase stability in the quaternary system.
However, the observed scaling of transition temperatures with differs
from that reported in the related ternary system Ni-Mn-Ga.Comment: 8 pages, 8 figures. Accepted for publication in the Physical Review
Sexual Function in Women Suffering from Aortoiliac Occlusive Disease
AbstractObjective:to describe the sexual function in women suffering aortoiliac occlusive disease (AIOD) and in an age-matched reference group.Patients and methods:thirty-six women suffering from AIOD were included. Twenty were investigated before vascular intervention (untreated) and 16 different women after treatment (treated). Eighteen age-matched women served as areferencegroup. The patients answered a questionnaire including sexual, social and medical questions and a gynaecological examination was performed.Results:untreated patients with AIOD have a significantly impaired physical well-being compared to the other groups (p<0.001). A negative effect of the vascular disease and its treatment on sexual life was experienced by 69% oftreatedcompared to 40% affected amonguntreated(p=0.05). Vulval sensibility was impaired in 44% oftreated, 11% ofuntreatedand 22% ofreferencepatients. Defective anal sphincter function was found in 33% oftreated, 17% ofuntreatedand 6% in thereferencegroup. Those differences were not statistically significant.Conclusions:symptomatic AIOD in women is associated with a significantly impaired physical and sexual well-being. Though limited by size and methodology, the results indicate the possibility of iatrogenic nerve damage
Relationships between two dimensions of employee perfectionism, postwork cognitive processing, and work day functioning
This daily diary study examined relations between two distinct perfectionism dimensions and work-related cognitions experienced by employees during evening leisure time. Drawing from perseverative cognitive processing theory, we hypothesized that perfectionistic concerns would be related to work-related worry and rumination during postwork evenings. In contrast, we hypothesized that a theoretically more adaptive perfectionist dimension (perfectionistic strivings) would be associated with positively valenced self-reflections about work across consecutive evenings. A sample of 148 full-time workers completed an initial survey, which included a trait perfectionism measure, reported their work-related cognitions across four consecutive evenings of a working week, rated their sleep quality immediately upon awakening on each subsequent morning, and their daily levels of emotional exhaustion and work engagement at the end of each work day. Results showed that perfectionistic concerns were indirectly negatively associated with sleep quality and work day functioning via the tendency to worry and ruminate about work. In contrast, perfectionistic strivings were indirectly positively associated with work day engagement via the propensity to experience positive thoughts about work during evening leisure time. The theoretical and practical implications of these findings are discussed
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