9,209 research outputs found
Фізика: лабораторний практикум
Present book contains theory ,description of experimental equipment ,procedure and analysis recommendations to the physics laboratory experiments for foreign students studying in Ukraine
Magnetohydrodynamic models of astrophysical jets
In this review, analytical results obtained for a wide class of stationary
axisymmetric flows in the vicinity of compact astrophysical objects are
analyzed, with an emphasis on quantitative predictions for specific sources.
Recent years have witnessed a great increase in understanding the formation and
properties of astrophysical jets. This is due not only to new observations but
also to advances in analytical theory which has produced fairly simple
relations, and to what can undoubtedly be called a breakthrough in numerical
simulation which has enabled confirmation of theoretical predictions. Of
course, we are still very far from fully understanding the physical processes
occurring in compact sources. Nevertheless, the progress made raises hopes for
near-future test observations that can give insight into the physical processes
occurring in active astrophysical objects.Comment: 40 pages, translated by K.A.Postnov, edited by A.Radzi
Highlights from galactic observations with MAGIC
MAGIC is one of the main instruments for exploring the galactic gamma-ray sky
from ground in the energy range of 50 GeV - 50 TeV. It consists of two 17 m
diameter imaging atmospheric Cherenkov telescopes located at the Roque de los
Muchachos Observatory, on the Canary island of La Palma. Thanks to its
excellent sensitivity, MAGIC has conducted relevant studies on galactic objects
of different types at Very High Energies. Among them, the Crab pulsar up to TeV
energies, the spectral cut-off of the supernova remnant Cassiopeia A, the
super-orbital variability of the binary system LSI +61 303, the search for
microqusars, multi-year observations of the Galactic Center and follow-up
studies of unidentified HAWC sources. In many cases, the results from these
observations challenge our understanding of the underlying emission mechanisms.
Here we review the latest results from the observation of these galactic
sources with MAGIC.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Transition Radiation of Moving Abrikosov Vortices
We show that Abrikosov vortices moving towards the surface of a
superconductor emit electromagnetic radiation into free space. The frequency
distribution of the radiated intensity displays a pronounced maximum at
microwave frequencies around v_x/lambda, where lambda is the magnetic
penetration length. Coherent motion of a lattice of flux lines leads to
constructive interference and increases the strength of the radiated power by a
large factor.Comment: 4 pages, 1 figure The new version includes a derivation of novel
dynamical London equations for a moving Abrikosov vortex, as well as a
detailed discussion of boundary condition
Object and Relation Centric Representations for Push Effect Prediction
Pushing is an essential non-prehensile manipulation skill used for tasks
ranging from pre-grasp manipulation to scene rearrangement, reasoning about
object relations in the scene, and thus pushing actions have been widely
studied in robotics. The effective use of pushing actions often requires an
understanding of the dynamics of the manipulated objects and adaptation to the
discrepancies between prediction and reality. For this reason, effect
prediction and parameter estimation with pushing actions have been heavily
investigated in the literature. However, current approaches are limited because
they either model systems with a fixed number of objects or use image-based
representations whose outputs are not very interpretable and quickly accumulate
errors. In this paper, we propose a graph neural network based framework for
effect prediction and parameter estimation of pushing actions by modeling
object relations based on contacts or articulations. Our framework is validated
both in real and simulated environments containing different shaped multi-part
objects connected via different types of joints and objects with different
masses. Our approach enables the robot to predict and adapt the effect of a
pushing action as it observes the scene. Further, we demonstrate 6D effect
prediction in the lever-up action in the context of robot-based hard-disk
disassembly.Comment: Project Page: https://fzaero.github.io/push_learning
Grasping, Perching, And Visual Servoing For Micro Aerial Vehicles
Micro Aerial Vehicles (MAVs) have seen a dramatic growth in the consumer market because of their ability to provide new vantage points for aerial photography and videography. However, there is little consideration for physical interaction with the environment surrounding them. Onboard manipulators are absent, and onboard perception, if existent, is used to avoid obstacles and maintain a minimum distance from them. There are many applications, however, which would benefit greatly from aerial manipulation or flight in close proximity to structures. This work is focused on facilitating these types of close interactions between quadrotors and surrounding objects. We first explore high-speed grasping, enabling a quadrotor to quickly grasp an object while moving at a high relative velocity. Next, we discuss planning and control strategies, empowering a quadrotor to perch on vertical surfaces using a downward-facing gripper. Then, we demonstrate that such interactions can be achieved using only onboard sensors by incorporating vision-based control and vision-based planning. In particular, we show how a quadrotor can use a single camera and an Inertial Measurement Unit (IMU) to perch on a cylinder. Finally, we generalize our approach to consider objects in motion, and we present relative pose estimation and planning, enabling tracking of a moving sphere using only an onboard camera and IMU
Computational Studies on Fluid and Particle Dynamics
This dissertation is divided into two parts. The first part includes chapter 2 to 4, which focus on development and application of numerical algorithm on particle and fluid simulation. Starting with a pure granular system in a driven cavity setup (Chapter 2), we move on to the immersed boundary simulation of fluid solid interaction (Chapter 3). This part ends with a coupled immersed boundary-discrete particle implementation. The second part includes Chapter 5 and Appendix A, each deals with an independent problem and focuses more on the theoretical aspects. Chapter 5 deals with a classic fluid dynamics problem of thermal wave induced net flux. Appendix A studies the underestimation of solver accuracy when the solution has singularities, and analyzes the cause of the underestimation using a simple theoretical model
Review of scientific topics for Millimetron space observatory
This paper describes outstanding issues in astrophysics and cosmology that
can be solved by astronomical observations in a broad spectral range from far
infrared to millimeter wavelengths. The discussed problems related to the
formation of stars and planets, galaxies and the interstellar medium, studies
of black holes and the development of the cosmological model can be addressed
by the planned space observatory Millimetron (the "Spectr-M" project) equipped
with a cooled 10-m mirror. Millimetron can operate both as a single-dish
telescope and as a part of a space-ground interferometer with very long
baseline.Comment: The translation of the original article in Physics Uspekhi
http://ufn.ru/ru/articles/2014/12/c
Skeletal status and soft tissue composition in astronauts. Tissue and fluid changes by radionuclide absorptiometry in vivo
A device has been constructed and tested which provides immediate readout of bone mineral content and bone width from absorptiometric scans with low energy radionuclides. The basis of this analog system is a logarithmic converter-integrator coupled with a precision linear ratemeter. The system provided accurate and reliable results on standards and ashed bone sections. Clinical measurements were made on about 100 patients with the direct readout system, and these were highly correlated with the results from digital scan data on the same patients. The direct readout system has been used successfully in field studies and surveys as well as for clinical observations
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