Traffic instabilities in self-organized pedestrian crowds

In human crowds as well as in many animal societies, local interactions among individuals often give rise to self-organized collective organizations that offer functional benefits to the group. For instance, flows of pedestrians moving in opposite directions spontaneously segregate into lanes of uniform walking directions. This phenomenon is often referred to as a smart collective pattern, as it increases the traffic efficiency with no need of external control. However, the functional benefits of this emergent organization have never been experimentally measured, and the underlying behavioral mechanisms are poorly understood. In this work, we have studied this phenomenon under controlled laboratory conditions. We found that the traffic segregation exhibits structural instabilities characterized by the alternation of organized and disorganized states, where the lifetime of well-organized clusters of pedestrians follow a stretched exponential relaxation process. Further analysis show that the inter-pedestrian variability of comfortable walking speeds is a key variable at the origin of the observed traffic perturbations. We show that the collective benefit of the emerging pattern is maximized when all pedestrians walk at the average speed of the group. In practice, however, local interactions between slow- and fast-walking pedestrians trigger global breakdowns of organization, which reduce the collective and the individual payoff provided by the traffic segregation. This work is a step ahead toward the understanding of traffic self-organization in crowds, which turns out to be modulated by complex behavioral mechanisms that do not always maximize the group's benefits. The quantitative understanding of crowd behaviors opens the way for designing bottom-up management strategies bound to promote the emergence of efficient collective behaviors in crowds.     

Ubiquitination Increases Parkin Activity to Promote Autophagic α-Synuclein Clearance

Parkinson’s disease (PD) is a movement disorder associated with genetic and age related causes. Although autosomal recessive early onset PD linked to parkin mutations does not exhibit α-Synuclein accumulation, while autosomal dominant and sporadic PD manifest with α-Synuclein inclusions, loss of dopaminergic substantia nigra neurons is a common denominator in PD. Here we show that decreased parkin ubiquitination and loss of parkin stability impair interaction with Beclin-1 and alter α-Synuclein degradation, leading to death of dopaminergic neurons. Tyrosine kinase inhibition increases parkin ubiquitination and interaction with Beclin-1, promoting autophagic α-Synuclein clearance and nigral neuron survival. However, loss of parkin via deletion increases α-Synuclein in the blood compared to the brain, suggesting that functional parkin prevents α-Synuclein release into the blood. These studies demonstrate that parkin ubiquitination affects its protein stability and E3 ligase activity, possibly leading to α-Synuclein sequestration and subsequent clearance.     

Phycoremediation potential,physiological, and biochemical response of <Emphasis Type="Italic">Amphora subtropica</Emphasis> and <Emphasis Type="Italic">Dunaliella</Emphasis> sp. to nickel pollution

Metal pollution can produce many biological effects on aquatic environments. The marine diatom Amphora subtropica and the green alga Dunaliella sp. possess a high metal absorption capacity. Nickel (Ni) removal by living cells of A. subtropica and Dunaliella sp. was tested in cultures exposed to different Ni concentrations (100, 200, 300, and 500 mg L^?1). The amount of Ni removed by the microalgae increased with the time of exposure and the initial Ni concentration in the medium. The metal, which was mainly removed by bioadsorption to Dunaliella sp. cell surfaces (93.63% of total Ni (for 500 mg Ni L^?1) and by bioaccumulation (80.82% of total Ni (for 300 mg Ni L^?1) into Amphora subtropica cells, also inhibited growth. Exposure to Ni drastically reduced the carbohydrate and protein concentrations and increased total lipids from 6.3 to 43.1 pg cell^?1, phenolics 0.092 to 0.257 mg GAE g^?1 (Fw), and carotenoid content, from 0.08 to 0.59 mg g^?1 (Fw), in A. subtropica. In Dunaliella sp., total lipids increased from 26.1 to 65.3 pg cell^?1, phenolics from 0.084 to 0.289 mg GAE g^?1 (Fw), and carotenoid content from 0.41 to 0.97 mg g^?1 (Fw). These compounds had an important role in protecting the algae against ROS generated by Ni. In order to cope with Ni stress shown by the increase of TBARS level, enzymatic (SOD, CAT, and GPx) ROS scavenging mechanisms were induced.     

Molecular dynamics study of the swelling patterns of Na/Cs-, Na/Mg-montmorillonites and hydration of interlayer cations

Over the last two decades, the swelling properties of montmorillonite (MMT) have been studied in many experimental and simulation works, but less attention has been given to MMT containing a mixture of monovalent/monovalent and monovalent/bivalent cations in the interlayer spaces. We carried out a molecular dynamics simulation of the swelling patterns of Na-, Mg-, Na/Cs-, Na/Mg-MMT in an isobaric isothermal ensemble (NPT) at T = 300 K and p = 1 atm. The simulation reproduced a swelling pattern of Na-, Mg-, Na/Cs-, Na/Mg-MMT and the swelling curves obtained showed the difference between the hydration mechanisms of the type of MMT used in this study. We also found out that the differences in size and hydration energy of Na, Cs and Na, Mg ions have strong implications on the structure of interlayer water. This has led to the difference in the swelling curves of the simulated Na-, Mg-, Na/Cs- and Na/Mg-MMT. For Na/Cs-MMT, the hydration energy of Na cations increased compared to that in Na-MMT, the hydration energy of Cs cations decreased in Na/Cs-MMT compared to that in Cs-MMT and also for Na/Mg-MMT, the hydration energy of Na cations increased compared to that in Na-MMT and that of Mg cations decreased in comparison with that in Mg-MMT. The diffusion coefficient of Cs cations obtained in this simulation was higher than that of Mg and Na cations in Cs-, Mg- and Na-MMT, respectively. Cesium cations have been seen to have a low hydration energy compared to Na and Mg cations and can be used as a good inhibitor of Na-MMT swelling process.     

Pressure treatment of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> in low-moisture environments

We investigated the influence of cell hydration on the ability of Saccharomyces cerevisiae CBS 1171 to withstand extreme hydrostatic pressure in order to determine the mechanisms involved in cell resistance. Hydration conditions were modified in two different ways. We first modulated the chemical potential of water by adding glycerol in cell suspensions. Another procedure consisted in dehydrating cells aerobically and immersing them in perfluorooctane, an innocuous hydrophobic liquid used as a pressure-transmitting medium, prior to pressure treatments. This original method made it possible to transmit isostatic pressure to yeast powders without changing the initial water activity (a _w) level at which cells had been equilibrated. The a _w ranged between 0.11 and 0.99. Pressure treatments were applied at levels of up to 600 MPa for 10 min, 24 h, and 6 days. The dehydration of cells was found to strongly limit, or even prevent, cell inactivation under pressure. Notably, cells suspended in a water–glycerol mixture with a _w levels of 0.71 or below were completely protected against all pressure treatments. Moreover, cells dehydrated aerobically survived for 6 days at 600 MPa even when a _w levels were relatively high (up to 0.94). We highlighted the crucial role of water content in determining cellular damage under pressure. When water is available in a sufficient amount, high pressure induces membrane permeabilization, causing uncontrolled mass transfers that could lead to death during a prolonged holding under pressure. Possible mechanisms of membrane permeabilization are discussed.