Quantum-secured blockchain

Blockchain is a distributed database which is cryptographically protected against malicious modifications. While promising for a wide range of applications, current blockchain platforms rely on digital signatures, which are vulnerable to attacks by means of quantum computers. The same, albeit to a lesser extent, applies to cryptographic hash functions that are used in preparing new blocks, so parties with access to quantum computation would have unfair advantage in procuring mining rewards. Here we propose a possible solution to the quantum era blockchain challenge and report an experimental realization of a quantum-safe blockchain platform that utilizes quantum key distribution across an urban fiber network for information-theoretically secure authentication. These results address important questions about realizability and scalability of quantum-safe blockchains for commercial and governmental applications.Comment: 7 pages, 2 figures; published versio

The Mass of the Compact Object in the X-Ray Binary Her X-1/HZ Her

We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H_gamma absorption line: mx=1.8Msun and mv=2.5Msun. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are mx=0.85\pm0.15Msun and mv=1.87\pm0.13Msun. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made.Comment: 20 pages, 4 tables, 8 figure

Presbyornithid bird

11 p. : ill., map ; 26 cm.Includes bibliographical references (p. 9-11).We describe a new large representative of the important fossil anseriform taxon Presbyornithidae from the latest Cretaceous (Maastrichtian) Nemegt Formation of southern Mongolia. This new taxon, Teviornis gobiensis, n. gen. et n. sp., is known from the associated manual portion of a right wing and the distal end of a right humerus, but is clearly diagnosable with respect to all other known representatives of the fossil Presbyornithidae. It is placed within the clades Anseriformes and Presbyornithidae, respectively, on the basis of a number of derived characters of the carpometacarpus and digits. Importantly, description of Teviornis confirms the presence of members of the neornithine clade Anseriformes ("waterfowl") in the late Cretaceous, as has been suggested previously on the basis of much less diagnostic fossil material as well as from clade divergence estimates founded on molecular sequence data. The extinct Presbyornithidae thus has a worldwide distribution and ranged in age from at least the Maastrichtian through to the uppermost Eocene

Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems

We present an analysis of over 2200 V images taken on 14 nights at the Mt. Laguna 1 m telescope of the open cluster M67. Our observations overlap but extend beyond the field analyzed by Gilliland et al. (1991), and complement data recently published by van den Berg et al. (2002) and Stassun et al. (2002). We show variability in the light curves of all 4 of the known W UMa variables on timescales ranging from a day to decades (for AH Cnc). We have modeled the light curve of AH Cnc, and the total eclipses allow us to determine q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near the turnoff of M67 makes it useful for constraining the turnoff mass for the cluster. We have also detected two unusual features in the light curve of AH Cnc that may be caused by prominences. We have also monitored cluster blue stragglers for variability, and we present evidence hinting at low level variations in the stragglers S752, S968, and S1263, and we place limits on the variability of a number of other cluster blue stragglers. Finally, we provide photometry of the sub-subgiant branch star S1063 showing variability on timescales similar to the orbital period, while the ``red straggler'' S1040 shows evidence of an unexplained drop in brightness at phases corresponding to the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A

Перспективы развития энергосберегающих способов дробления хрупких материалов

Crushing machines are part of the charge departments of blastfurnace and steelmaking shops of metallurgical enterprises. One of the main indicator of the crushing process is its energy efficiency. It is determined by the mass of crushed material when consuming a unit of electricity. The article considers various methods of crushing brittle materials and the design of crushing machines for their implementation. The analysis of the crushers has shown that impact crushers are the most energyefficient. However, due to a significant drawback (the yield of a suitable product is very small), they are practically not used in the metallurgical industry, in which high requirements are imposed on the finished product fractional composition. In the metallurgical industry, compression crushers are widely used with approximately the same specific energy intensity, that is, with the same energy consumption for the destruction of a unit volume of material of equal strength. Compression fracture is the most energy intensive crushing method known. In singleroll crushers, a piece of material is fed into the gap between a roll and a solid, stationary plate. During the operation a complex stress state is generated in the destructed material. Compressive forces act on a piece of crushed material, causing normal compressive stresses in it, and an internal torque, causing shear stresses. This is achieved by the reduction in energy on crushing by 20 - 30 % in comparison with crushers operating in compression (all other things are equal). The authors describe the design of a crusher, in which the destruction of the processed material occurs due to the forces acting on the crushed piece in one plane towards each other. In this case, only shear stresses arise in the processed piece. The use of crushers, in which the destruction of the processed material occurs due to generation of only tangential stresses in a piece, can reduce the energy consumption per unit of finished product by almost a half. The design of such crushers is a promising direction in the development of machines intended for crushing. © 2021 National University of Science and Technology MISIS. All rights reserved

Prospects for Energy-Saving Methods of Crushing Brittle Materials

Crushing machines are part of the charge departments of blast-furnace and steel-making shops of metallurgical enterprises. One of the main indicator of the crushing process is its energy efficiency. It is determined by the mass of crushed material when consuming a unit of electricity. The article considers various methods of crushing brittle materials and the design of crushing machines for their implementation. The analysis of the crushers has shown that impact crushers are the most energy-efficient. However, due to a significant drawback (the yield of a suitable product is very small), they are practically not used in the metallurgical industry, in which high requirements are imposed on the finished product fractional composition. In the metallurgical industry, compression crushers are widely used with approximately the same specific energy intensity, that is, with the same energy consumption for the destruction of a unit volume of material of equal strength. Compression fracture is the most energy-intensive crushing method known. In single-roll crushers, a piece of material is fed into the gap between a roll and a solid, stationary plate. During the operation, a complex stress state is generated in the destructed material. Compressive forces act on a piece of crushed material, causing normal compressive stresses in it, as well as an internal torque causing shear stresses. This is achieved by the reduction in energy on crushing by 20–30% in comparison with crushers operating in compression (all other things are equal). The authors describe the design of a crusher, in which the destruction of the processed material occurs due to the forces acting on the crushed piece in one plane towards each other. In this case, only shear stresses arise in the processed piece. The use of crushers, in which the destruction of the processed material occurs due to generation of only tangential stresses in a piece, can reduce the energy consumption per unit of finished product by almost a half. The design of such crushers is a promising direction in the development of machines intended for crushing. © 2021, Allerton Press, Inc

Two-body quantum mechanical problem on spheres

The quantum mechanical two-body problem with a central interaction on the sphere ${\bf S}^{n}$ is considered. Using recent results in representation theory an ordinary differential equation for some energy levels is found. For several interactive potentials these energy levels are calculated in explicit form.Comment: 41 pages, no figures, typos corrected; appendix D was adde