The emergence of design in pedestrian dynamics: Locomotion, self-organization, walking paths and constructal law

Metareview: a survey of active matter reviews

In the past years, the amount of research on active matter has grown extremely rapidly, a fact that is reflected in particular by the existence of more than 1000 reviews on this topic. Moreover, the field has become very diverse, ranging from theoretical studies of the statistical mechanics of active particles to applied work on medical applications of microrobots and from biological systems to artificial swimmers. This makes it very difficult to get an overview over the field as a whole. Here, we provide such an overview in the form of a metareview article that surveys the existing review articles and books on active matter. Thereby, this article provides a useful starting point for finding literature about a specific topic.

Evolution and irreversibility: Two distinct phenomena and their distinct laws of nature

To clarify the place of time direction of change in nature (time arrow), the present article shows why Evolution and Irreversibility are two distinct phenomena. Their distinct laws of nature are the Constructal Law and the Second Law, respectively. The demonstration is based on the simplest setting imaginable: a solid body moving in a pool of water. The view is holistic: the system selected for analysis is the body and the pool, not the body alone, and the phenomenon is the evolution of the image (configuration) of the whole. New is also the answer to the question of what flows in this evolving flow configuration. Along the way, important terms are defined: phenomenon, law, irreversibility, nature, design, freedom, theory versus empiricism, information, knowledge, selection, purpose, engine, refrigeration, and wheel. More complex natural settings for the demonstration are in the second part of the article: engines, refrigeration, heating and cooling, the wheel, and a pushed boat sliding on water.

Convergent Evolution of Boats with Sails

This article unveils the geometric characteristics of boats with sails of many sizes, covering the range 10²–10⁵ kg. Data from one hundred boat models are collected and tabulated. The data show distinct trends of convergent evolution across the entire range of sizes, namely: (i) the proportionality between beam and draft, (ii) the proportionality between overall boat length and beam, and (iii) the proportionality between mast height and overall boat length. The review shows that the geometric aspect ratios (i)–(iii) are predictable from the physics of evolution toward architectures that offer greater flow access through the medium.

Gender and age differences in components of traffic-related pedestrian death rates: exposure, risk of crash and fatality rate

Background

This ecological study aimed i) to quantify the association of age and gender with the three components of pedestrians’ death rates after a pedestrian-vehicle crash: exposure, risk of crash and fatality, and ii) to determine the contribution of each component to differences in death rates according to age and gender in Spain.

Methods

We analyzed data for 220 665 pedestrians involved in road crashes recorded in the Spanish registry of road crashes with victims from 1993 to 2011, and a subset of 39 743 pedestrians involved in clean collisions (in which the pedestrian did not commit an infraction). Using decomposition and quasi-induced exposure methods, we obtained the proportion of increase in death rates for each age and gender group associated with exposure, risk of collision and fatality.

Results

Death rates increased with age. The main contributor to this increase was fatality, although exposure also increased with age. In contrast, the risk of collision decreased with age. Males had higher death rates than females, especially in the 24–54 year old group. Higher fatality rates in males were the main determinant of this difference, which was also related with a higher risk of collision in males. However, exposure rates were higher in females.

Conclusions

The magnitude and direction of the associations between age and gender and each of the three components of pedestrians’ death rates differed depending on the specific component explored. These differences need to be taken into account in order to prioritize preventive strategies intended to decrease mortality among pedestrians.

Electronic supplementary material

The online version of this article (doi:10.1186/s40621-016-0079-2) contains supplementary material, which is available to authorized users.

Rolling stones and turbulent eddies: why the bigger live longer and travel farther

Here we report the discovery that even the simplest, oldest and most prevalent forms of evolutionary movement—rolling bodies and whirls of turbulence—exhibit the same body-size effect on life time and life travel as the evolutionary movement united by the body-size effect so far: animals, rivers, vehicles, jets and plumes. In short, the bigger should last longer and travel farther. For rolling bodies, the life span (t) and the life travel (L) should increase with the body mass (M) raised to the powers 1/6 and 1/3, respectively. The number of rolls during this movement is constant, independent of body size. For an eddy of turbulence, t should increase with the eddy mass (M) raised to the power 2/3, while L should increase with M^2/3 times the bulk speed of the turbulent stream that carries the eddy. The number of rolls during the eddy life span is a constant independent of eddy size.

Physics' insights into pedestrian motion and crowd dynamics: reply to comments on "The emergence of design in pedestrian dynamic: locomotion, self-organization, walking paths and constructal law"

Pedestrians' world is not a static one, but rather one which is constantly in flux. The pedestrian dynamics is subject to a wide range of influences and displays an interesting phenomenology. Along with collective self-organization phenomena (e.g., streams of people, rivers of people, collective synchronization), there are also a multitude of applications in the context of crowd management, design of pedestrian facilities and urban planning. Here, I address comments from the discussants of my review paper from the viewpoint of elementary physics laws paying particular attention to the self-organization phenomena in crowds.