Boundary Layer Self-Similar Solution for the Hot Radiative Accretion onto a Rapidly Spinning Neutron Star

We consider hot accretion onto a rapidly spinning neutron star (or any other compact object with a surface). A radiative hot settling flow has been discovered at low accretion rates in the early work by Medvedev & Narayan (2001) and analytical solution has been presented. It was shown later that this flow can match external medium smoothly, thus enforcing its physical feasibility. Here we complete the study of the global structure of such hot accretion by presenting the analytical solution for the boundary later, which forms between the bulk of the flow and the stellar surface. We confirm our results via full numerical solution of height-integrated two-temperature hydrodynamic equations.Comment: 14 pages, 1 figure. accepted for publication in Ap

THE STUDY OF PATH-FOLLOWING ACCURACY OF ROBOTIC SINGLE-ROTOR HELICOPTER

In this paper we study the accuracy of a single-rotor robotic small-scale helicopter flight along a complex path. The control algorithms for the autopilot are synthesized using the position-trajectory control approach. We use hardware-software complex to test the helicopter autopilot. The simulation in hardware-software complex is used to debug the autopilot software and complex study of autopilot control algorithms in early development stages without full-scale experiments. The paper shows results of the simulation of single-rotor small-scale helicopter flight

Transparent dense sodium

Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium and sodium, leading in turn to structurally complex phases and superconductivity with a high critical temperature. But the most intriguing prediction - that the seemingly simple metals Li and Na will transform under pressure into insulating states, owing to pairing of alkali atoms - has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at 200 GPa (corresponding to 5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.Comment: Published in Nature 458, 182-185 (2009

Search for critical phenomena in Pb - Pb collisions

NA44 uses a 512 channel Si pad array covering $1.5 <\eta < 3.3$ to study charged hadron production in Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, by simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we look for a possible critical behaviour in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing.NA44 uses a 512 channel Si pad array covering $1.5 <\eta < 3.3$ to study charged hadron production in Pb+Pb collisions at the CERN SPS. We apply a multiresolution analysis, based on a Discrete Wavelet Transformation, to probe the texture of particle distributions event-by-event, by simultaneous localization of features in space and scale. Scanning a broad range of multiplicities, we look for a possible critical behaviour in the power spectra of local density fluctuations. The data are compared with detailed simulations of detector response, using heavy ion event generators, and with a reference sample created via event mixing

An Approximating Mathematical Model of Interaction Between a Freely Rotating Disk and Soil

A generalized mathematical model of disk interaction with soil was built under general assumptions regarding the mode of the disk knife motion in soil, namely, in a mode of slippage, skidding or rolling without slippage and skidding. Previously constructed models follow from it as particular cases at certain values of parameters. However, because of computational complexity of this model for the case of a freely rotating disk knife consisting in the need for a preliminary numerical solution of a transcendental equation to determine the mode of disk motion, the generalized mathematical model has not found wide application. Therefore, an analytical two-dimensional approximation of a generalized model of disk interaction with soil which is a new model of approximation type was constructed on the basis of a computer experiment using the least squares method.An explicit expression was obtained for the kinematic parameter of a freely rotating disk knife which determines its mode of motion. It was established that this parameter is a rational function of relative depth of the disk penetration and the dimensionless dynamic coefficient characterizing soil properties. Also, explicit expressions were obtained for the projections of the resultant soil reaction forces acting on the blade of the disk knife and its side faces depending on the data of dimensionless parameters. It has been established that the horizontal component of the reaction which determines tractive resistance of the disk is also a rational function of the relative penetration depth and the dimensionless dynamic coefficient. It was established that the magnitude of the kinematic parameter significantly affects the magnitude and direction of the resultant soil reactions to the disk. The expressions obtained make it possible to significantly simplify experiments to determine the resultant soil reaction forces to a freely rotating disk knife and reduce their required number. These expressions make it possible to carry out strength calculations of soil-cultivating working tools with disks and determine their optimal parameters according to the strength criteria and the minimum specific energy consumption with accuracy sufficient for engineering practice. Adequacy of the obtained expressions was confirmed by comparison with experimental data of the disk knife dynamometr

Development of Dimensionally Stable Structures of Multilayer Pipelines and Cylindrical Pressure Vessels From Carbon Fiber Reinforced Plastic

In the framework of the momentless theory of cylindrical thin shells, the elastic deformation of multilayer pipes and pressure vessels is investigated. It is assumed that the pipes and pressure vessels are made by two-way spiral winding of carbon fiber reinforced plastic tape on a metal mandrel.The analysis of the dependences of elastic deformations on the reinforcement angles is performed. The relations for axial and circumferential deformations of the wall, depending on the structure of the layer package, reinforcement angles under static loading are obtained. The separate and combined effect of internal pressure and temperature is considered. For the separate effect of loads, the graphs of deformations against the winding angle are plotted.Composite pipes made of KMU-4L carbon fiber reinforced plastic, as well as composite metal-composite pipes, are investigated. The results obtained for thermal loads are in good agreement with the data of the known experiment and solution. Depending on the load parameters, composite and metal-composite structures with dimensionally stable properties are determined.It is shown that dimensionally stable structures can be used to solve the problem of compensation of elastic deformations of pipelines. For this purpose, using the ASCP software package, the variant analysis of model structures is performed. By the comparative analysis of the three versions of the structure, layer package structures and reinforcement schemes, ensuring a significant reduction of loads on the supporting elements are obtained. On the example of a pipeline with a flowing fluid, it is shown that the use of dimensionally stable multilayer pipes makes it possible to eliminate bending deformations and significantly reduce the level of working forces and stresses.Dimensionally stable composite multilayer pipes open up new approaches to the design of pipelines and pressure vessels. It is possible to create structures with predetermined (not necessarily zero) displacement fields, consistent with the fields of the initial technological displacements, as well as with the displacements of conjugate elastic elements and equipment when the operating mode changes. The scope of such structures is not limited to "hot" pipes. The results can be used in cryogenic engineerin

Introducing the DREAMS Project: DaRk mattEr and Astrophysics with Machine learning and Simulations

We introduce the DREAMS project, an innovative approach to understanding the astrophysical implications of alternative dark matter models and their effects on galaxy formation and evolution. The DREAMS project will ultimately comprise thousands of cosmological hydrodynamic simulations that simultaneously vary over dark matter physics, astrophysics, and cosmology in modeling a range of systems -- from galaxy clusters to ultra-faint satellites. Such extensive simulation suites can provide adequate training sets for machine-learning-based analyses. This paper introduces two new cosmological hydrodynamical suites of Warm Dark Matter, each comprised of 1024 simulations generated using the Arepo code. One suite consists of uniform-box simulations covering a $(25~h^{-1}~{\rm M}_\odot)^3$ volume, while the other consists of Milky Way zoom-ins with sufficient resolution to capture the properties of classical satellites. For each simulation, the Warm Dark Matter particle mass is varied along with the initial density field and several parameters controlling the strength of baryonic feedback within the IllustrisTNG model. We provide two examples, separately utilizing emulators and Convolutional Neural Networks, to demonstrate how such simulation suites can be used to disentangle the effects of dark matter and baryonic physics on galactic properties. The DREAMS project can be extended further to include different dark matter models, galaxy formation physics, and astrophysical targets. In this way, it will provide an unparalleled opportunity to characterize uncertainties on predictions for small-scale observables, leading to robust predictions for testing the particle physics nature of dark matter on these scales