6 research outputs found
Analyzing Stop-and-Go Waves by Experiment and Modeling
The main topic of this paper is the analysis and modeling of stop-and-go
waves, observable in experiments of single lane movement with pedestrians. The
velocity density relation using measurements on a 'microscopic' scale shows the
coexistence of two phases at one density. These data are used to calibrate and
verify a spatially continuous model. Several criteria are chosen that a model
has to satisfy: firstly we investigated the fundamental diagram (velocity
versus density) using different measurement methods. Furthermore the
trajectories are compared to the occurrence of stop-and-go waves qualitatively.
Finally we checked the distribution of the velocities at fixed density against
the experimental one. The adaptive velocity model introduced satisfies these
criteria well.Comment: Fifth International Conference on Pedestrian and Evacuation Dynamics,
March 8-10, 2010, National Institute of Standards and Technology,
Gaithersburg, MD US
Fast Molecular Compression by a Hyperthermal Collision Gives Bond-Selective Mechanochemistry
Using electrospray ion beam deposition, we collide the complex molecule Reichardt’s Dye (C41H30NO+) at low, hyperthermal translational energy (2 - 50 eV) with a Cu(100) surface and image the outcome at single-molecule level by scanning tunneling microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (sub-ps) is much shorter than the thermalization timescale (ns), thereby yielding reaction products that are unobtainable thermally
Large wood debris contributes to beach ecosystems but colombian beachgoer’s do not recognize it
Large Woody Debris (LWD) accumulation serves essential ecological functions and benefits society’s coastal ecosystems (e.g., beaches). Thus far, the ecosystem services perspective has paid little attention to LWD. Therefore, we aim to contrast social perceptions on LWD and its ecological significance in Puerto Velero beach, Caribbean, Colombia. In consequence, the contribution of LWD to the conformation and creation of Puerto Velero beach was analyzed, as well as how beachgoers perceive the importance of LWD and if they were willing to pay to remove LWD in this beach. To achieve this, a quantitative convergent approach was then proposed using GIS analysis and remote sensing to understand the contributions of LWD to the Puerto Velero beach ecosystem; and in addition, a survey was performed to determine how beachgoers perceived LWD and how they valued the phenomenon. Results indicate that LWD contributed to beach maintenance; nevertheless, most people neglected LWD values because of its lack of visual attractiveness. As such, ecosystem services targets become conflicted because people positively perceived ecosystem services provided by beaches, but they did not assign importance to the beach dynamics they deemed unattractive, regardless of their vast importance
Pedestrian Dynamics: From Empirical Results to Modeling
In this contribution, we review the state of the art of the interplay between empirical and theoretical studies of pedestrian dynamics. First, we introduce the main physical quantities characterizing the properties of a homogeneous crowd. A brief summary of some important empirical findings is given. Finally, we discuss the properties of microscopic pedestrian models. Different classifications of the models are proposed. We emphasize the relevance of empirical results and show how they can be used for validation and calibration