By means of simple dynamical experiments we study the combined effect of gravitational and gas dynamics in the evolution of an initially out-of-equilibrium, uniform, and rotating massive overdensity thought of as in isolation. The rapid variation of the system mean-field potential makes the pointlike particles (PPs), which interact only via Newtonian gravity, form a quasistationary thick disk dominated by rotational motions surrounded by far out-of-equilibrium spiral arms. On the other side, the gas component is subjected to compression shocks and radiative cooling so as to develop a much flatter disk, where rotational motions are coherent and the velocity dispersion is smaller than that of PPs. Around such gaseous disk long-lived, but nonstationary, spiral arms form: these are made of gaseous particles that move coherently because have acquired a specific phase-space correlation during the gravitational collapse phase. Such a phase-space correlation represents a signature of the violent origin of the arms and implies both the motion of matter and the transfer of energy. On larger scales, where the radial velocity component is significantly larger than the rotational one, the gas follows the same out-of-equilibrium spiral arms traced by PPs. We finally outline the astrophysical and cosmological implications of our results.
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http://dx.doi.org/10.1103/PhysRevE.102.042108 | DOI Listing |
Micromachines (Basel)
November 2024
School of Mechatronics Engineering, Henan University of Science and Technology, Luoyang 471003, China.
The actuator is a critical component of the micromanipulator. By utilizing the properties of expansion and contraction, the piezoelectric actuator enables the manipulator to handle and grasp miniature objects during micromanipulation. However, in piezoelectric ceramic disc actuators with conventional surface electrode configurations, the actuating force generated in the radial direction is relatively limited.
View Article and Find Full Text PDFHum Immunol
November 2024
Hematology and Oncology Research Center, Non-communicable Diseases Research Institute, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Electronic address:
Purpose: The study aimed to investigate the connection between an intronic variant in the ABO gene (rs657152) and the severity of COVID-19 in terms of clinical symptoms, haematological complications, inflammatory markers, and lung lesions.
Methods: After applying exclusion criteria, the study included 240 patients divided into 3 groups: 88 Outpatients, 84 Ward-hospitalized, and 68 ICU-admitted/failed patients. The tetra-ARMS PCR method was used to genotype ABO polymorphism in the patient.
Nature
September 2024
Astrobiology Center, National Institutes of Natural Sciences, Mitaka, Japan.
The canonical theory for planet formation in circumstellar disks proposes that planets are grown from initially much smaller seeds. The long-considered alternative theory proposes that giant protoplanets can be formed directly from collapsing fragments of vast spiral arms induced by gravitational instability-if the disk is gravitationally unstable. For this to be possible, the disk must be massive compared with the central star: a disk-to-star mass ratio of 1:10 is widely held as the rough threshold for triggering gravitational instability, inciting substantial non-Keplerian dynamics and generating prominent spiral arms.
View Article and Find Full Text PDFSoft Matter
August 2024
Department of Theoretical Physics, Complutense University of Madrid, 28040 Madrid, Spain.
We examine the influence of density on the transition between chain and spiral structures in planar assemblies of active semiflexible filaments, utilizing detailed numerical simulations. We focus on how increased density, and higher Péclet numbers, affect the activity-induced transition spiral state in a semiflexible, self-avoiding active chain. Our findings show that increasing the density causes the spiral state to break up, reverting to a motile chain-like shape.
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