160 research outputs found
Combinatorial optimization model for railway engine assignment problem
This paper presents an experimental study for the Hungarian State Railway Company (M\'AV). The engine assignment problem was solved at M\'AV by their experts without using any explicit operations research tool. Furthermore, the operations research model was not known at the company. The goal of our project was to introduce and solve an operations research model for the engine assignment problem on real data sets. For the engine assignment problem we are using a combinatorial optimization model. At this stage of research the single type train that is pulled by a single type engine is modeled and solved for real data. There are two regions in Hungary where the methodology described in this paper can be used and M\'AV started to use it regularly. There is a need to generalize the model for multiple type trains and multiple type engines
On the apsidal motion of BP Vulpeculae
BP Vulpeculae is a bright eclipsing binary system showing apsidal motion. It
was found in an earlier study that it shows retrograde apsidal motion which
contradicts theory. In this paper we present the first light curve of the
system and its light curve solution as well as seven new times of the minima
from the years 1959-1963. This way we could expanded the baseline of the
investigation to five decades. Based on this longer baseline we concluded that
the apsidal motion is prograde agreeing with the theoretical expectations and
its period is about 365 years and the determined internal structure constant is
close to the theoretically expected one.Comment: accepted for New Astronomy; two figure
Investigation of Allotropic Ăâα-Sn Transition in High Tin Content Solder Alloys with Different Microscopy and Spectroscopy Techniques
In the microelectronics, ÎČ-Sn (white tin) is the base material of the solder alloys and surface finishes. The so-called âtin pestâ phenomenon is the spontaneous allotropic transition of Ă-Sn to the semiconductor α-Sn (gray tin) below 13.2°C. In this work, different microscopy and spectroscopy techniques were applied to characterize the tin pest phenomenon in the case of different solder alloys and inoculator materials as well as to study the applicability of these techniques in tin pest research. The optical imaging technique was used to compare the surface marks of the allotropic transition in the case of different inoculator materials. The development of the transition towards the sample bodies was studied on metallurgical cross-sections. Electrical resistance measurements were applied to determine the different phases of the transition in the case of different alloys and inoculators. The grain sliding and α -Sn expansion during the transition was observed by scanning electron microscopy and focused ion beam - scanning ionic microscopy. The ratio of the transitioned tin and the duration of the transition process was determined by Mössbauer spectroscopy. Our results have shown that the transition phases can considerably differ at the different alloys and inoculators, like different nucleation, growth, and the saturation phase. The accurate characterization of the transition in the given material combinations is possible only with the combined application of the applied analytical methods
Weighted network modules
The inclusion of link weights into the analysis of network properties allows
a deeper insight into the (often overlapping) modular structure of real-world
webs. We introduce a clustering algorithm (CPMw, Clique Percolation Method with
weights) for weighted networks based on the concept of percolating k-cliques
with high enough intensity. The algorithm allows overlaps between the modules.
First, we give detailed analytical and numerical results about the critical
point of weighted k-clique percolation on (weighted) Erdos-Renyi graphs. Then,
for a scientist collaboration web and a stock correlation graph we compute
three-link weight correlations and with the CPMw the weighted modules. After
reshuffling link weights in both networks and computing the same quantities for
the randomised control graphs as well, we show that groups of 3 or more strong
links prefer to cluster together in both original graphs.Comment: 19 pages, 7 figure
Simulating Dynamical Features of Escape Panic
One of the most disastrous forms of collective human behaviour is the kind of
crowd stampede induced by panic, often leading to fatalities as people are
crushed or trampled. Sometimes this behaviour is triggered in life-threatening
situations such as fires in crowded buildings; at other times, stampedes can
arise from the rush for seats or seemingly without causes. Tragic examples
within recent months include the panics in Harare, Zimbabwe, and at the
Roskilde rock concert in Denmark. Although engineers are finding ways to
alleviate the scale of such disasters, their frequency seems to be increasing
with the number and size of mass events. Yet, systematic studies of panic
behaviour, and quantitative theories capable of predicting such crowd dynamics,
are rare. Here we show that simulations based on a model of pedestrian
behaviour can provide valuable insights into the mechanisms of and
preconditions for panic and jamming by incoordination. Our results suggest
practical ways of minimising the harmful consequences of such events and the
existence of an optimal escape strategy, corresponding to a suitable mixture of
individualistic and collective behaviour.Comment: For related information see http://angel.elte.hu/~panic,
http://www.helbing.org, http://angel.elte.hu/~fij, and
http://angel.elte.hu/~vicse
Uncovering the overlapping community structure of complex networks in nature and society
Many complex systems in nature and society can be described in terms of
networks capturing the intricate web of connections among the units they are
made of. A key question is how to interpret the global organization of such
networks as the coexistence of their structural subunits (communities)
associated with more highly interconnected parts. Identifying these a priori
unknown building blocks (such as functionally related proteins, industrial
sectors and groups of people) is crucial to the understanding of the structural
and functional properties of networks. The existing deterministic methods used
for large networks find separated communities, whereas most of the actual
networks are made of highly overlapping cohesive groups of nodes. Here we
introduce an approach to analysing the main statistical features of the
interwoven sets of overlapping communities that makes a step towards uncovering
the modular structure of complex systems. After defining a set of new
characteristic quantities for the statistics of communities, we apply an
efficient technique for exploring overlapping communities on a large scale. We
find that overlaps are significant, and the distributions we introduce reveal
universal features of networks. Our studies of collaboration, word-association
and protein interaction graphs show that the web of communities has non-trivial
correlations and specific scaling properties.Comment: The free academic research software, CFinder, used for the
publication is available at the website of the publication:
http://angel.elte.hu/clusterin
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