Efficient Flocking: Metric Versus Topological Interactions

Flocking is a fascinating phenomenon observed across a wide range of living organisms. We investigate, based on a simple self-propelled particle model, how the emergence of ordered motion in a collectively moving group is influenced by the local rules of interactions among the individuals, namely, metric versus topological interactions as debated over in the current literature. In the case of the metric ruling, the individuals interact with the neighbours within a certain metric distance; in contrast, in the topological ruling, interaction is confined within a number of fixed nearest neighbours. Here, we explore how the range of interaction versus the number of fixed interacting neighbours affects the dynamics of flocking in an unbounded space, as observed in natural scenarios. Our study reveals the existence of a certain threshold value of the interaction radius in the case of metric ruling and a threshold number of interacting neighbours for the topological ruling to reach an ordered state. Interestingly, our analysis shows that topological interaction is more effective in bringing the order in the group, as observed in field studies. We further compare how the nature of the interactions affects the dynamics for various sizes and speeds of the flock.

Efficient flocking: metric versus topological interactions

Flocking is a fascinating phenomenon observed across a wide range of living organisms. We investigate, based on a simple self-propelled particle model, how the emergence of ordered motion in a collectively moving group is influenced by the local rules of interactions among the individuals, namely, metric versus topological interactions as debated in the current literature. In the case of the metric ruling, the individuals interact with the neighbours within a certain metric distance; by contrast, in the topological ruling, interaction is confined within a number of fixed nearest neighbours. Here, we explore how the range of interaction versus the number of fixed interacting neighbours affects the dynamics of flocking in an unbounded space, as observed in natural scenarios. Our study reveals the existence of a certain threshold value of the interaction radius in the case of metric ruling and a threshold number of interacting neighbours for the topological ruling to reach an ordered state. Interestingly, our analysis shows that topological interaction is more effective in bringing the order in the group, as observed in field studies. We further compare how the nature of the interactions affects the dynamics for various sizes and speeds of the flock.

EMERGENCE OF ORDERED MOTION OF THE OSCILLATOR DRIVEN BY FLUCTUATING FORCE

Computational experiments with double pendulum, Tacker’s oscillator and steel beam, described by Duffing equations, are performed. We assume that a fluid drives the oscillator by fluctuating force. The considered complex motion is a combination of deterministic chaos and stochasticity. If amount of the fluctuating force is large enough (the number of fluid particles interacting with the oscillator is then large), oscillator motion becomes ordered. Similar result is obtained in the Lorenz model, when considering a part of the Earth atmosphere interacting with surrounding air.

Pair formation in insect swarms driven by adaptive long-range interactions

In swarms of flying insects, the motions of individuals are largely uncoordinated with those of their neighbours, unlike the highly ordered motion of bird flocks. However, it has been observed that insects may transiently form pairs with synchronized relative motion while moving through the swarm. The origin of this phenomenon remains an open question. In particular, it is not known if pairing is a new behavioural process or whether it is a natural by-product of typical swarming behaviour. Here, using an ‘adaptive-gravity’ model that proposes that insects interact via long-range gravity-like acoustic attractions that are modulated by the total background sound (via ‘adaptivity’ or fold-change detection) and that reproduces measured features of real swarms, we show that pair formation can indeed occur without the introduction of additional behavioural rules. In the model, pairs form robustly whenever two insects happen to move together from the centre of the swarm (where the background sound is high) towards the swarm periphery (where the background sound is low). Due to adaptivity, the attraction between the pair increases as the background sound decreases, thereby forming a bound state since their relative kinetic energy is smaller than their pair-potential energy. When the pair moves into regions of high background sound, however, the process is reversed and the pair may break up. Our results suggest that pairing should appear generally in biological systems with long-range attraction and adaptive sensing, such as during chemotaxis-driven cellular swarming.

Complex Dynamics and Statistics of 1-D Hamiltonian Lattices: Long Range Interactions and Supratransmission

In this paper, I review a number of results that my co-workers and I have obtained in the field of 1-Dimensional (1D) Hamiltonian lattices. This field has grown in recent years, due to its importance in revealing many phenomena that concern the occurrence of chaotic behavior in conservative physical systems with a high number of degrees of freedom. After the establishment of the Kolomogorov-Arnol'd-Moser (KAM) theory in the 1960s, a wealth of results were obtained about such systems as small perturbations of completely integrable Ndegree- of-freedom Hamiltonians, where ordered motion is dominant in the form of invariant tori. Since the 1980s, however, and particularly in the last two decades, there has been great progress in understanding the properties of Hamiltonian 1D lattices far from the KAM regime, where "weak" and "strong" forms of chaos begin to play an increasingly significant role. It is the purpose of this review to address and highlight some of these advances, in which the author has made several contributions concerning the dynamics and statistics of these lattices.

VLA and ALMA observations of the lensed radio-quiet quasar SDSS J0924+0219: a molecular structure in a 3 μJy radio source

ABSTRACT We present Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimetre Array (ALMA) observations of SDSS J0924+0219, a z = 1.524 radio-quiet lensed quasar with an intrinsic radio flux density of about 3 $\, \mu$Jy. The four lensed images are clearly detected in the radio continuum and the CO(5–4) line, whose centroid is at z = 1.5254 ± 0.0001, with a marginal detection in the submillimetre continuum. The molecular gas displays ordered motion, in a structure approximately 1–2.5 kpc in physical extent, with typical velocities of 50–100 km s−1. Our results are consistent with the radio emission being emitted from the same region, but not with a point source of radio emission. SDSS J0924+0219 shows an extreme anomaly in the flux ratios of the two merging images in the optical continuum and broad emission lines, suggesting the influence of microlensing by stars in the lensing galaxy. We find the flux ratio in the radio, submillimetre continuum and CO lines to be slightly greater than 1 but much less than that in the optical, which can be reproduced with a smooth galaxy mass model and an extended source. Our results, supported by a microlensing simulation, suggest that the most likely explanation for the optical flux anomaly is indeed microlensing.

Ionized gas kinematics of massive elliptical galaxies in CALIFA and in cosmological zoom-in simulations

Context. Powerful active galactic nuclei (AGN) are supposed to play a key regulatory role on the evolution of their host galaxies by shaping the thermodynamic properties of their gas component. However, little is known as to the nature and the visibility timescale of the kinematical imprints of AGN-driven feedback. Gaining theoretical and observational insights into this subject is indispensable for a thorough understanding of the AGN-galaxy coevolution and could yield empirical diagnostics for the identification of galaxies that have experienced a major AGN episode in the past. Aims. We present an investigation of kinematical imprints of AGN feedback on the warm ionized gas medium (WIM) of massive early-type galaxies (ETGs). To this end, we take a two-fold approach that involves a comparative analysis of Hα velocity fields in 123 local ETGs from the CALIFA (Calar Alto Legacy Integral Field Area Survey) integral field spectroscopy survey with 20 simulated galaxies from high-resolution hydrodynamic cosmological SPHgal simulations. The latter were resimulated for two modeling setups, one with and another without AGN feedback. Methods. In order to quantify the effects of AGN feedback on gas kinematics, we measured three parameters that probe deviations from simple regular rotation by using the kinemetry package. These indicators trace the possible presence of distinct kinematic components in Fourier space (k3, 5/k1), variations in the radial profile of the kinematic major axis (σPA), and offsets between the stellar and gas velocity fields (Δϕ). These quantities were monitored in the simulations from a redshift 3 to 0.2 to assess the connection between black hole accretion history, stellar mass growth, and the kinematical perturbation of the WIM. Results. Observed local massive galaxies show a broad range of irregularities, indicating disturbed warm gas motions, which is irrespective of being classified via diagnostic lines as AGN or not. Simulations of massive galaxies with AGN feedback generally exhibit higher irregularity parameters than without AGN feedback, which is more consistent with observations. Besides AGN feedback, other processes like major merger events or infalling gas clouds can lead to elevated irregularity parameters, but they are typically of shorter duration. More specifically, k3, 5/k1 is most sensitive to AGN feedback, whereas Δϕ is most strongly affected by gas infall. Conclusions. We conclude that even if the general disturbance of the WIM velocity is not a unique indicator for AGN feedback, irregularity parameters that are high enough to be consistent with observations can only be reproduced in simulations with AGN feedback. Specifically, an elevated value for the deviation from simple ordered motion is a strong sign for previous events of AGN activity and feedback.

Kinematics of simulated galaxies II: Probing the stellar kinematics of galaxies out to large radii

ABSTRACT We investigate the stellar kinematics of a sample of galaxies extracted from the hydrodynamic cosmological Magneticum Pathfinder simulations out to five half-mass radii. We construct differential radial stellar spin profiles quantified by the observationally widely used λ and the closely related (V/σ) parameters. We find three characteristic profile shapes: profiles exhibiting a (i) peak within 2.5 half-mass radii and a subsequent decrease; (ii) continuous increase that plateaus at larger radii typically with a high amplitude; (iii) completely flat behaviour typically with low amplitude, in agreement with observations. This shows that the kinematic state of the stellar component can vary significantly with radius, suggesting a distinct interplay between in-situ star formation and ex-situ accretion of stars. Following the evolution of our sample through time, we provide evidence that the accretion history of galaxies with decreasing profiles is dominated by the anisotropic accretion of low-mass satellites that get disrupted beyond ∼2.0 half-mass radii, building up a stellar halo with non-ordered motion while maintaining the central rotation already present at z = 2. In fact, at z = 2 decreasing profiles are the predominant profile class. Hence, we can predict a distinct formation pathway for galaxies with a decreasing profile and show that the centre resembles an old embedded disc. Furthermore, we show that the radius of the kinematic transition provides a good estimation for the transition radius from in-situ stars in the centre to accreted stars in the halo.

CHANGES IN HEMOMICROCIRCULATORY BED OF RAT ILEUM MUCOSA IN TRANSPLANTATION OF CRYOPRESERVED PLACENTA AGAINST THE BACKGROUND OF ACUTE ASEPTIC INFLAMMATION OF PERITONEUM

Hemomicrocirculatory bed (HMCB) in the modern sense is a complex organized system that provides ordered motion of blood, tissue fluids, absorption and excretion of biochemical substrates, metabolites, biologically active substances. Among the interrelated and interdependent processes in the system of HMCB, the main role belongs to the patterns of blood circulation in the vessels. The last decade has been marked by a completely new approach to solving problems associated with impaired blood filling. The use of tissue transplantation, in particular cryopreserved placenta grafts, as a corrective method, is quite effective. The latter was the basis for a comprehensive study of the ileal mucosa HMCB response to the cryopreserved placenta transplantation [11]. The aim of this study was to investigate the dynamics of the ileum mucosa hemo-microcirculatory bed parameters with a single administration of cryopreserved placenta and with the cryopreserved placenta administration against the background of acute aseptic experimental peritoneum inflammation in rats. Object and methods of the study. The object of the experimental study was the ileum wall sampled from 140 mature Wistar male rats. The animals were divided into four groups. Animals were euthanized on the 1st, 2nd, 3rd, 5th, 7th, 10th, 14th, 21st, 30th days. Measurements of the HMCB vessels internal diameter in the ileac mucosa were performed. The mathematical processing was performed by means of Student's t test (t). Differences at p <0.05 were considered reliable. Transplantation of cryopreserved placenta causes the reaction of all links of the hemomicrocirculatory bed by increasing their average diameter with maximum values for 5 days. Simulation of acute aseptic inflammation of the peritoneum initially led to a decrease in the diameter of arterioles by 5% and capillaries by 2.3%, by 2-3 days, and then by an increase in their diameters, by the 14th day of the study. During the experiment, the venular unit increased in diameter by the 14th day of the study. When transplanting cryopreserved placenta against acute aseptic inflammation of the peritoneum of the arterioles by 4% and capillaries by 2%, they first decrease in diameter by 2 days, and then increase in diameter by 3-10 days of the study. During the experiment, the venular unit significantly increased in diameter by the 14th day of the study. With the introduction of cryopreserved placenta on the background of acute aseptic inflammation of the peritoneum, the realization of inflammation decreased by 4-5 days.