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Analysis of X-Ray Emission from OB Stars. IV. About X-Ray Emission from Inhomogeneous Winds of OB Stars

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Research in Astronomy and Astrophysics 2023年第10期23卷 387-405页

作者： Elizaveta Ryspaeva alexander kholtygin Crimean Astrophysical Observatory NauchnyCrimeaRussia Saint-Petersburg State University Saint-PetersburgRussia

We study the origin of X-ray emission from OB stars due to collisions of stellar winds and/or inhomogeneities in the winds. The low-resolution X-ray spectra of a big sample of OB stars were fitted by both the stationary APEC/MEKAL models and by this model with an additional PSHOCK component describing the nonstationary X-ray emission. These spectra were also described by two-temperature PSHOCK models. More than ~50% of considered spectra can be described by the above-mentioned model combinations including the PSHOCK model and the quality of the fits appears to be better for O stars. The plasma temperature of the PSHOCK component is about 1–5 keV with the ionization timescale τ_(u)~ 10^(8)–10^(13)s cm^(-3). The temperature of the PSHOCK component increases with the momentum and kinetic energy of the stellar wind by a power law with an index ~0.12–*** dependencies were not revealed through modeling by the stationary APEC/MEKAL models only. At the same time the X-ray luminosity of OB stars depends on momentum and kinetic energy of their winds similarly either for stationary or for nonstationary models. We conclude that many O stars and some B stars can be sources of the nonstationary X-rays formed in their inhomogeneous stellar wind.

关键词： stars:early-type stars:statistics X-rays:stars

Analysis of the X-ray emission of OB stars:O stars

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Research in Astronomy and Astrophysics 2018年第8期18卷 121-134页

作者： Elizaveta Ryspaeva alexander kholtygin Main(Pulkovo)Astronomical Observatory 196140 Saint PetersburgRussia Saint Petersburg State University 198504 Saint PetersburgRussia

We investigate the global properties of X-ray emission from O stars, analyzing the X-ray spec- tra of 32 O stars from archival data of the XMM-Newton space observatory. We examine two hypotheses about of the origin of X-ray emission from O stars. The first is a paradigm proposed by Pollock, that was revealed from an analysis of the （ Ori X-ray observation. The second is the magnetically confined wind-shock （MCWS） model. For checking Pollock＇s hypothesis, we determine the distribution of the ratio of half width at half maximum （HWHM） to the wind terminal velocity for lines in spectra of all examined stars. In addition, we check three probable consequences from the MCWS model. We analyze if a correlation exists between the spectral hardness and such stellar parameters as the wind terminal velocity, stellar magnetic field and mass loss rate. The result showed that Pollock＇s hypothesis is not correct. We also established that not all consequences of the MCWS model considered by us are con- firmed. In addition, our spectral analysis method indicated that O stars probably have clumped stellar winds with spherical clumps.

关键词： stars early-type - stars spectra X-ray

Analysis of the X-ray emission from OB stars Ⅲ: low-resolution spectra of OB stars

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Research in Astronomy and Astrophysics 2020年第7期20卷 161-171页

作者： Elizaveta Ryspaeva alexander kholtygin Crimean Astrophysical Observatory NauchnyCrimea 298409Russia Saint-Petersburg State University Saint-Petersburg 198504Russia Institute of Astronomy Russian Academy of Sciencesul.Pyatniskaya 48Moscow 119017Russia

This paper is the third in our series of papers devoted to the investigation of X-ray emission from OB *** our two previous papers,we study the high-resolution X-ray spectra of 32 O stars and 25 B stars to investigate the correlations between the properties of X-ray emission and stellar *** checked if the X-ray hardness and post-shock plasma temperature grow with increasing stellar magnetic field,mass loss rate and terminal wind *** previous analysis of high-resolution spectra showed that the correlations are weak or even *** the present paper,we analyzed low-resolution X-ray spectra,using model-independent X-ray hardness values for checking the above mentioned *** establish that X-ray luminosities LX weakly depend on the stellar magnetic *** the same time,Lx ∝ M0.5 and LX ∝ Ekin0.5,where M is the mass loss rate and Ekin is the kinetic energy of the *** X-ray luminosities decrease with growing magnetic confinement parameter η.We also argue that there is an additional(probably non-thermal) component contributed to the stellar X-ray emission.

关键词： stars:early-type stars:spectra:X-Ray

Testing and modelling of transient adhesion phenomena in rolling-sliding contacts

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Friction 2024年第5期12卷 1016-1027页

作者： Daniel KVARDA alexander MEIERHOFER Klaus SIX Faculty of Mechanical Engineering Brno University of TechnologyBrno61669Czech Republic Virtual Vehicle Research GmbH Graz8010Austria

Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track *** is of high importance specifically when these effects result in critically low adhesion,which poses a risk to traction and braking of railway *** study presents a model that can replicate the transient changes of the coefficient of adhesion with tested water and solid particle *** experimental data for the model are measured using a commercial ball-on-disc *** experimental results showed a liquid reservoir in front of the contact area that slowly reduces in *** observation was used in the modelling approach to divide the calculation into two stages where the reservoir is present and when it *** model was able to reproduce the occurrence of low adhesion region seen in experimental results with different particle concentrations.

关键词： coefficient of adhesion tribology transient effects wheel-rail contact

Competitive Resource Allocation Among Urban Congestion Areas in a Modern Big City

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Journal of the Operations Research Society of China 2024年第1期12卷 133-153页

作者： alexander Krylatov Anastasiya Raevskaya Institute of Applied Mathematical Research of the Karelian Research Centre of the Russian Academy of Sciences Petrozavodsk185910Russia Saint Petersburg State University Saint Petersburg199034Russia

The continuing growth of modern big cities leads to their spatial expansion and the emergence of new road connections and urban *** where large transportation flows of pedestrians,passengers,and drivers come together create demand points,which attract business companies that strive to allocate their resources in the most sought-after ***,the law of supply and demand restrains companies from allocating all their resources solely in the most popular congestion areas since the more valuable an urban area,the higher the cost to be paid for a resource unit allocation *** a result,companies act in a non-cooperative manner and try to minimize their own overall costs when allocating resources across available commercial areas in a big ***-cooperative behavior of companies leads to the problem of Nash equilibrium search in the game of competing *** this paper,we study the corresponding resource allocation game under affine cost functions and obtain Nash equilibrium strategies in explicit *** findings allow us to develop a simple procedure for computing Nash equilibria in the game of companies allocating their resources among urban congestion *** computational study demonstrates the dependence of the average price for resource allocation on the number of players and their resource *** outcome of the paper contributes to flow theory and seems to be fresh and useful for managers.

关键词： Resource allocation Nash equilibrium Affine costs

A Converse Theorem for Split SO_(2l) over Finite Fields

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Acta Mathematica Sinica,English Series 2024年第3期40卷 731-771页

作者： alexander HAZELTINE Bai Ying LIU Department of Mathematics Purdue University150 N.University St.West LafayetteIN 47907USA E-mail:ahazelti@purdue.edu liu2053@purdue.edu

We prove a converse theorem for split even special orthogonal groups over finite *** is the only case left on converse theorems of classical groups and the difficulty is the existence of the outer automorphism. In thi... 详细信息

关键词： Converse theorems generic cuspidal representations even special orthogonal groups

Architecture of Graphics System with 3D Acceleration Support for Embedded Operating Systems

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Tsinghua Science and Technology 2024年第3期29卷 863-873页

作者： alexander Giatsintov Kirill Mamrosenko Pavel Bazhenov Center of Visualization and Sattelite Information Technologies Scientific Research Institute for System Analysis of the Russian Academy of Sciences(SRISA RAS)Moscow 117218Russia

An increasing number of tasks now require the use of hardware accelerators to reduce the time required for computation and display the computational *** paper presents a new graphics system architecture for operating systems(OSs)with microkernel architecture,including real-time *** proposed system architecture provides capabilities for displaying graphical images on various information display devices and for accelerating graphical operations on *** architecture of the graphics system uses a concept of allocators to manage system and video memory,provides an abstraction of memory operations with a single interface for video memory management,and simplifies memory handling where incorrect operation is the cause of many failures.A comparison between the performance of a real-time OS and Linux OS implementing the graphics system using the example of a glmark2 benchmark is presented,thereby the superiority of the proposed architecture in several scenarios is demonstrated.

关键词： real-time operating system(RTOS) graphics system rendering system architecture operatingsystem visualization system programming

Unveiling the atomic-scale transition between light harvesting and photoprotective states in plant photosynthesis

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Science China Chemistry 2024年第5期67卷 1375-1377页

作者： alexander V.Ruban School of Biological and Behavioural Sciences Queen Mary University of LondonLondon E14NSUK

Non-photochemical chlorophyll fluorescence quenching(NPQ) stands as a cornerstone in the realm of photosynthesis research, attracting generations of dedicated scientists in their quest to unravel its mysteries. This mechanism, crucial for safeguarding photosynthesis, plays a pivotal role in regulating light harvesting, particularly in oxygenic photosynthesis where the oxygen-evolving photosystem II (PSII)is susceptible to photodamage [1].

关键词： harvesting protective attracting

Prediction of ball-on-plate friction and wear by ANN with data-driven optimization

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Friction 2024年第6期12卷 1235-1249页

作者： alexander KOVALEV Yu TIAN Yonggang MENG State Key Laboratory of Tribology in Advanced Equipment Tsinghua UniversityBeijing 100084China

For training artificial neural network(ANN),big data either generated by machine or measured from experiments are used as input to"learn"the unspecified functions defining the *** experimental data are fed directly into the optimizer allowing training to be performed according to a predefined loss *** predict sliding friction and wear at mixed lubrication conditions,in this study a specific ANN structure was so designed that deep learning algorithms and data-driven optimization models can be *** ball-on-plate friction and wear data were analyzed using the specific training procedure to optimize the weights and biases incorporated into the neural layers of the ANN,and only two independent experimental data sets were used during the ANN optimization *** the training procedure,the ANN is capable to predict the contact and hydrodynamic pressure by adapting the output data according to the tribological condition implemented in the optimization algorithm.

关键词： machine learning deep learning artificial neural network mixed lubrication