1,018 research outputs found
Methods for measuring pedestrian density, flow, speed and direction with minimal scatter
The progress of image processing during recent years allows the measurement
of pedestrian characteristics on a "microscopic" scale with low costs. However,
density and flow are concepts of fluid mechanics defined for the limit of
infinitely many particles. Standard methods of measuring these quantities
locally (e.g. counting heads within a rectangle) suffer from large data
scatter. The remedy of averaging over large spaces or long times reduces the
possible resolution and inhibits the gain obtained by the new technologies.
In this contribution we introduce a concept for measuring microscopic
characteristics on the basis of pedestrian trajectories. Assigning a personal
space to every pedestrian via a Voronoi diagram reduces the density scatter.
Similarly, calculating direction and speed from position differences between
times with identical phases of movement gives low-scatter sequences for speed
and direction. Closing we discuss the methods to obtain reliable values for
derived quantities and new possibilities of in depth analysis of experiments.
The resolution obtained indicates the limits of stationary state theory.Comment: 16 pages, 10 figs, submitted to Physica
Language classification from bilingual word embedding graphs
We study the role of the second language in bilingual word embeddings in
monolingual semantic evaluation tasks. We find strongly and weakly positive
correlations between down-stream task performance and second language
similarity to the target language. Additionally, we show how bilingual word
embeddings can be employed for the task of semantic language classification and
that joint semantic spaces vary in meaningful ways across second languages. Our
results support the hypothesis that semantic language similarity is influenced
by both structural similarity as well as geography/contact.Comment: To be published at Coling 201
Promotions and Incentives: The Case of Multi-Stage Elimination Tournaments
Promotion tournaments play an important role for the provision of incentives in firms. In this paper, we extend research on single-stage rank-order tournaments and analyze behavior in multi-stage elimination tournaments. The main treatment of our laboratory experiment is a two-stage tournament in which equilibrium efforts are the same in both stages. We compare this treatment to a strategically equivalent one-stage tournament and to another two-stage tournament with a more convex wage structure. Confirming previous findings average effort in our one-stage treatment is close to Nash equilibrium. In contrast, subjects in our main treatment provide excess effort in the first stage both with respect to Nash predictions and compared to the equivalent one-stage tournament. The results for the more convex two-stage tournament show that excess effort in the first stage is a robust finding and that subjects react only weakly to differences in the wage structure.personnel economics, tournament, incentives, laboratory experiment
Implicit Contracts, Unemployment, and Labor Market Segmentation
We analyze the impact of imperfect contract enforcement on the emergence of unemployment. In an experimental labor market where trading parties can form long-term employment relationships, we compare a work environment where effort is observable, but not verifiable to a situation where explicit contracts are feasible. Our main result shows that unemployment is much higher when third-party contract enforcement is absent. Unemployment is involuntary, being caused by firms' employment and contracting policy. Moreover, we show that implicit contracting can lead to a segmentation of the labor market. Firms in both segments earn similar profits, but workers in the secondary sector face much less favorable conditions than their counterparts in primary-sector jobs.incentives, implicit contracts, unemployment, fairness, dual labor markets
Cyclic volcanism at convergent margins: linked to aarth orbital parameters or climate changes?
EGU2010-13373
The frequency of volcanic activity varies on a wide rangeof spatial and temporal scales, from <1 yr. periodicities in single volcanic systems to periodicities of 106 yrs. in global volcanism. The causes of these periodicities are poorly understood although the long-term global variations are likely linked to plate-tectonic processes. Here we present evidence for temporal changes in eruption frequencies at an intermediate time scale (104 yrs.) using the Pleistocene to recent records of widespread tephras of sub-Plinian to Plinian, and occasionally co-ignimbrite origin, along the Pacific Ring of Fire, which accounts for about half of the global length of 44,000 km of active subduction. Eruptions at arc volcanoes tend to be highly explosive and the well-preserved tephra records from the ocean floor can be assumed to be representative of how eruption frequencies varied with time. Volcanic activity along the Pacific Ring of Fire evolved through alternating phases of high and low frequency; although there is modulation by local and regional geologic conditions, these variations have a statistically significant periodicity of 43 ka that overlaps with the temporal variation in the obliquity of the Earth’s rotation axis, an orbital parameter that also exerts a strong control on global climate changes. This may suggest that the frequency of volcanic activity is controlled by effects of global climate changes. However, the strongest physical effects of climate change occur at 100 ka periods which are not seen in the volcanic record. We therefore propose that the frequency of volcanic activity is directly influenced by minute changes in the tidal forces induced by the varying obliquity resulting in long-period gravitational disturbances acting on the upper mantle
The repulsive force in continous space models of pedestrian movement
Pedestrian movements can be modeled at different degrees of detail. While
flux models (Predeshensky/Milinski 1971) and cellular automata models
(Schreckenberg 2002) give answers to some important questions and are fast and
easy to use, continuous space modeling has the potential of full flexibility in
geometry and realistic description of individual movements in arbitrary fine
resolution. While the acceleration forces in these models are known with good
reliability, there is no agreement on the repulsive forces, not even on the
functional form of these forces (Lakoba 2005, Molnar 1996, Parisi 2005, Yu
2005). We give some basic consideration to define the minimal complexity of the
functional form of the repulsive forces together with some estimates of the
values of parameters. From these considerations it becomes obvious that the
repulsive forces have to depend not only on the relative position of persons,
but also on the speeds and speed differences. The parameters of these forces
will be situation dependant. They can in principle be derived from video
observations of people moving, although the large scatter of data and the
complexity involved makes for large uncertainties.Comment: 6 pages, 5 figures, keywords: pedestrian movement, fundamental
diagram, social force mode
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