Flocking at the edge of chaos

Recent investigations have provided important insights into the complex structure and dynamics of collectively moving flocks of living organisms. Two intriguing observations are, scale-free correlations in the velocity fluctuations, in the presence of a high degree of order, and topological distance mediated interactions. Understanding these features, especially, the origin of fluctuations, appears to be challenging in the current scheme of models. It has been argued that flocks are poised at criticality. We present a self-propelled particle model where neighbourhoods and forces are defined through topology based rules. The force fluctuations occur spontaneously, and gives rise to scale-free correlations in the absence of noise and in the presence of alignment of velocities. We characterize the behaviour of the model through power spectral densities and the Lyapunov spectrum. Our investigations suggest self-organized criticality as a probable route to the existence of criticality in flocks.Comment: 6 pages, 5 figure

Aggregation of self-propelled particles with sensitivity to local order

We study a system of self-propelled particles (SPPs) in which individual particles are allowed to switch between a fast aligning and a slow nonaligning state depending upon the degree of the alignment in the neighborhood. The switching is modeled using a threshold for the local order parameter. This additional attribute gives rise to a mixed phase, in contrast to the ordered phases found in clean SPP systems. As the threshold is increased from zero, we find the sudden appearance of clusters of nonaligners. Clusters of nonaligners coexist with moving clusters of aligners with continual coalescence and fragmentation. The behavior of the system with respect to the clustering of nonaligners appears to be very different for values of low and high global densities. In the low density regime, for an optimal value of the threshold, the largest cluster of nonaligners grows in size up to a maximum that varies logarithmically with the total number of particles. However, on further increasing the threshold the size decreases. In contrast, for the high density regime, an initial abrupt rise is followed by the appearance of a giant cluster of nonaligners. The latter growth can be characterized as a continuous percolation transition. In addition, we find that the speed differences between aligners and nonaligners is necessary for the segregation of aligners and nonaligners.Comment: 11 pages, 7 figure

Modelling exposure between populations using networks of mobility during COVID-19

The use of mobile phone call detail records and device location data for the calling patterns, movements, and social contacts of individuals, have proven to be valuable for devising models and understanding of their mobility and behaviour patterns. In this study we investigate weighted exposure networks of human daily activities in the capital region of Finland as a proxy for contacts between postal code areas during the pre-pandemic year 2019 and pandemic years 2020, 2021 and early 2022. We investigate the suitability of gravity and radiation type models for reconstructing the exposure networks based on geo-spatial and population mobility information. For this we use a mobile phone dataset of aggregated daily visits from a postal code area to cellphone grid locations, and treat it as a bipartite network to create weighted one mode projections using a weighted co-occurrence function. We fit a classical gravity model and a radiation model to the averaged weekly and yearly projection networks with geo-spatial and socioeconomic variables of the postal code areas and their populations. We also consider an extended gravity type model comprising of additional postal area information such as distance via public transportation and population density. The results show that the co-occurrence of human activities, or exposure, between postal code areas follows both the gravity and radiation type interactions, once fitted to the empirical network. The effects of the pandemic beginning in 2020 can be observed as a decrease of the overall activity as well as of the exposure of the projected networks. These effects can also be observed in the network structure as changes towards lower clustering and higher assortativity. Evaluating the parameters of the fitted models over time shows on average a shift towards a higher exposure of areas in closer proximity as well as a higher exposure towards areas with larger population. In general, the results show that the postal code level networks changed to be more proximity weighted after the pandemic began, following the government imposed non-pharmaceutical interventions, with differences based on the geo-spatial and socioeconomic structure of the areas

Comparative analysis of fine and nanoparticles for cellular uptake, oxidative stress and genomic damage in human lung cells

The study was done to demonstrate that nanoparticles are more toxic than fine particles, even if they have the same chemical composition. The toxicity of a particle within a single cellular system is dependent on several properties including shape, size, chemical composition, and surface charge along with the intrinsic biological pathways activated in a cell following their uptake. The higher toxicity by nanoparticles compared to fine particles having the same chemical composition is due to the higher density of surface molecules presenting them with a higher surface charge and a larger surface area to react. A Fe(III) nanoparticle behaves like a catalyst providing the space and the proper environment for the biomolecules to react with oxidizing elements. Due to the special properties nanoparticles retain. Their utilization will increase leading to the advancement of nanotechnology in almost every industrial sector. In view of the potential toxic effects of these particles it must be recommended, that special care should be taken during their production to minimize the exposure of workers. Special emphasis should be laid on the charge and intracellular retention properties when nanoparticles are used for medical purposes such as thermal imaging and cancer drug targeting. This recommendation should be specially implemented for the poorly soluble nanoparticles made out of inorganic compounds such as the iron-containing nanoparticles

Quercetin as an antiviral weapon-A review

Antioxidants are substances that can prevent cells from the damage caused by unstable molecules such as free radicals. Quercetin, a plant pigment present in many fruits, vegetables, grains, and one of the most beneficial antioxidants in the diet and plays an important role in helping the body and prevent free radical damage, which is linked to chronic diseases. The antioxidant properties of quercetin may help to reduce inflammation, allergy symptoms, blood pressure. A lot of studies have been done and experiments have been conducted both in vivo and in vitro and it has been found that in cultured cells many respiratory viruses were inhibited by quercetin. At a minimal inhibitory concentration of 0.03 to 0.5μg/ml in WI-38 or Hela cells, Cytopathic effects produced by echovirus type 7,11,12,19, rhinovirus, poliovirus, and coxsackievirus A21 and B1 were inhibited. The plaque formed by DNA and RNA viruses such as Herpes Simplex Virus-1, Polio type 1, and parainfluenza types 3 were effectively reduced demonstrating its anti-replicative properties. This article reviews effect of quercetin on different types of viral infections