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The Dependence of Stellar Activity Cycles on Effective Temperature

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Research in Astronomy and Astrophysics 2022年第12期22卷 198-210页

作者： leonid Kitchatinov Institute of Solar-Terrestrial Physics SB RAS Lermontov Str.126AIrkutsk 664033Russia

This paper proposes the idea that the observed dependence of stellar activity cycles on rotation rate can be a manifestation of a stronger dependence on the effective temperature. Observational evidence is recalled and theoretical arguments are given for the presence of cyclic activity in the case of sufficiently slow rotation only. Slow rotation means proximity to the observed upper bound on the rotation period of solar-type stars. This maximum rotation period depends on temperature and shortens for hotter stars. The maximum rotation period is interpreted as the minimum rotation rate for operation of a large-scale dynamo. A combined model for differential rotation and the dynamo is applied to stars of different mass rotating with a rate slightly above the threshold rate for the *** show shorter dynamo cycles for hotter stars. As the hotter stars rotate faster, the computed cycles are also shorter for faster rotation. The observed smaller upper bound for rotation period of hotter stars can be explained by the larger threshold amplitude of the α-effect for onset of their dynamos: a larger α demands faster rotation. The amplitude of the(cycling) magnetic energy in the computations is proportional to the difference between the rotation period and its upper bound for the dynamo. Stars with moderately different rotation rates can differ significantly in super-criticality of their dynamos and therefore in their magnetic activity, as observed.

关键词： dynamo stars:activity stars:magnetic field stars:solar-type stars:rotation

Mechanisms Modeling the Double Rotation of the Elytra in Beetles （Coleoptera）

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Journal of Bionic Engineering 2011年第4期8卷 395-405页

作者： leonid Frantsevich Schmalhausen-Institute of Zoology B. Chmielnicki str. 15 Kiev-3 O 01601 Ukraine

We recorded transient movements, i.e. opening and closing, of beetle elytra. The beetles were tethered from below and filmed under a skew mirror; two markers were glued on each elytron at the apex and at the base. Body-fixed 3D traces of the apical and basal markers were reconstructed. The trace of the basal marker was, as a rule, non-parallel to the apical trace. The costal edge of the elytron uniformly supinated in the course of adduction of the apical marker. We found two essential attributes of double rotation：（1） the elytron to body articulation is approximately a spherical mechanism; （2） transient opening and closing possess single degree of freedom. The double rotation was modeled with two mechanisms：（1） a flexagon model of the Haas and Wootton＇s type simulated the elytral movement relative to the movement of one facet of the flexagon; （2） a screw and nut model provided traces as two sectors of a helical thread, one sector was phase shifted with respect to other one. Screw guideways in a spherical mechanism give rise to discrepancies. Exact solution for a spherical mechanism with two guideways was proposed. The modeling revealed the attribute （3）： the elytron is actuated by two linked but differently directed drives. Experimental investigations on the elytron to body articulation may be oriented at search of those mechanisms.

关键词： insect flight insect thorax flexagon screw and nut joint

Computational study of laser fragmentation in liquid:Phase explosion,inverse Leidenfrost effect at the nanoscale,and evaporation in a nanobubble

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Science China(Physics,Mechanics & Astronomy) 2022年第7期65卷 99-114页

作者： Hao Huang leonid V.Zhigilei School of Mechanical Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China Department of Materials Science and Engineering University of VirginiaCharlottesville 22904-4745USA

Laser fragmentation in liquid is an effective and environment-friendly processing technique capable of yielding colloidal nanoparticles and atomic clusters with a narrow size distribution. The advancement of this technique can be facilitated by an improved understanding of processes that control the sizes, shapes, and structures of the produced nanoparticles. In this work, the dependence of the fragmentation mechanisms on the energy density deposited by the laser pulse is investigated in atomistic simulations performed for 20 nm Au nanoparticles irradiated in water by 10 ps laser pulses. The simulations reveal that the decrease in the absorbed laser energy leads to sequential transitions from the regime of “strong” phase explosion, when all products of an explosive phase decomposition of the irradiated nanoparticle are promptly injected into the water surrounding a nanobubble formed around the nanoparticle, to two distinct regimes of nanoparticle fragmentation leading to the formation of a large central nanoparticle surrounded by smaller satellite fragments. First, in the regime of “mild” phase explosion, the central nanoparticle is produced by the reflection of some of the hot metal droplets generated by the explosive decomposition of the nanoparticle from the boundary of the nanobubble. This reflection is attributed to the inverse Leidenfrost effect acting at the nanoscale. The reflected droplets converge in the center of the nanobubble and coalesce into a single droplet that solidifies shortly after the collapse of the nanobubble. Further decrease in the absorbed laser energy brings the irradiation conditions below the threshold for the phase explosion and results in the formation of a core-satellite structure of the fragmentation products through an interplay of the intense evaporation from the surface of the irradiated nanoparticle, evolution of the nanobubble, and condensation of the metal vapor into clusters and small satellite nanoparticles. The computationa

关键词： laser fragmentation in liquid molecular dynamics simulations phase explosion inverse Leidenfrost effect nanobubble nanoparticles

Nonlinear interference in crystal superlattices

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Light(Science & Applications) 2020年第1期9卷 1239-1245页

作者： Anna V.Paterova leonid A.Krivitsky Institute of Materials Research and Engineering(IMRE) Agency for Science Technology and Research(A*STAR)138634 SingaporeSingapore

Nonlinear interferometers with correlated photons hold promise to advance optical characterization and metrology techniques by improving their performance and *** interferometers offer subshot noise phase sensitivity and enable measurements in detection-challenging regions using inexpensive and efficient *** sensitivity of nonlinear interferometers,defined by the ability to measure small shifts of interference fringes,can be significantly enhanced by using multiple nonlinear elements,or crystal ***,to date,experiments with more than two nonlinear elements have not been realized,thus hindering the potential of nonlinear ***,we build a nonlinear interferometer with up to five nonlinear elements,referred to as superlattices,in a highly stable and versatile *** study the modification of the interference pattern for different configurations of the superlattices and perform a proof-of-concept gas sensing experiment with enhanced *** approach offers a viable path towards broader adoption of nonlinear interferometers with correlated photons for imaging,interferometry,and spectroscopy.

关键词： spectroscopy nonlinear Nonlinear

Utilization of Extrinsic Fabry-Perot Interferometers with Spectral Interferometric Interrogation for Microdisplacement Measurement

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Journal of Electronic Science and Technology 2020年第1期18卷 59-75页

作者： leonid Liokumovich Aleksandr Markvart Nikolai Ushakov Higher School of Applied Physics and Space Technologies Peter the Great St.Petersburg Polytechnic UniversitySt.Petersburg 195251

The paper presents a number of signal processing approaches for the spectral interferometric interrogation of extrinsic Fabry-Perot interferometers(EFPIs). The analysis of attainable microdisplacement resolution is performed and the analytical equations describing the dependence of resolution on parameters of the interrogation setup are derived. The efficiency of the proposed signal processing approaches and the validity of analytical derivations are supported by experiments. The proposed approaches allow the interrogation of up to four multiplexed sensors with attained resolution between 30 pm and 80 pm, up to three times improvement of microdisplacement resolution of a single sensor by means of using the reference interferometer and noisecompensating approach, and ability to register signals with frequencies up to 1 kHz in the case of 1 Hz spectrum acquisition rate. The proposed approaches can be used for various applications, including biomedical, industrial inspection, and others, amongst the microdisplacement measurement.

关键词： Absolute measurement dynamic measurement Fabry-Perot interferometer least-squares methods optical fiber sensors resolution analysis resolution enhancement sensor multiplexing spectral interferometry

Computational fluid dynamics simulations of aerosol behavior in a high-speed (Heubach) rotating drum dustiness tester

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Particuology 2023年第1期72卷 68-80页

作者： Hongyu Chen Milind A.Jog leonid A.Turkevich Thermal-Fluids and Thermal Processing Lab Mechanical&Materials EngineeringUniversity of CincinnatiCincinnatiOH 45221-0072USA Division of Field Studies and Engineering(DFSE) National Institute for Occupational Safety&Health(NIOSH)The Centers for Disease Control&Prevention(CDC)Alice Hamilton Laboratory1090 Tusculum AvenueCincinnatiOH 45226USA

Potential exposure from hazardous dust may be assessed by evaluating the dustiness of the powders being *** is the tendency of a powder to aerosolize with a given input of *** we used computational fluid dynamics(CFD)to numerically investigate the flow inside the European Standard(EN15051)rotating drum dustiness tester during its *** present work extends those CFD studies to the widely used Heubach rotating *** flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model;the aerosol is incorporated via a Euler-Lagrangian multiphase *** air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent *** spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls;at high rotation rates,the axial jet becomes *** flow behavior qualitatively differs from the stable EN15051 flow *** aerodynamic instability promotes efficient mixing within the Heubach drum,resulting in higher particle capture efficiencies for particle sizes d<80μm.

关键词： Rotating drum Dustiness Euler-Lagrangian multiphase AKN k-epsilon turbulence

Artificial intelligence applications in finance:a survey

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Journal of Management Analytics 2023年第4期10卷 676-692页

作者： Xuemei Li Alexander Sigov leonid Ratkin leonid A.Ivanov Ling Li Department of Information Technology and Decision Sciences Strome College of BusinessOld Dominion UniversityNorfolkVAUSA Department of Electronic Machinery University of Electronic Science and Technology of ChinaChengduPeople’s Republic of China Russian Technological University MoscowRussian Federation Russian Academy of Sciences MoscowRussian Federation Russian Academy of Engineering MoscowRussian Federation

Finance is in our daily *** invest,borrow,lend,budget,and save *** also provides guidelines for corporation and government spending and revenue *** statistical solutions such as regression,PCA,and CFA have been widely used in financial forecasting and *** the increasing interest in artificial intelligence in recent years,this paper reviews the Artificial Intelligence(AI)techniques in the finance domain systematically and attempts to identify the current AI technologies used,major applications,challenges,and trends in *** explores AI-related articles in Finance in IEEE Xplore and EI compendex *** suggest AI has been engaged in Finance in financial forecasting,financial protection,and financial analysis and decision-making *** forecasting is one of the main sub-fields of Finance affected by AI *** major AI technology used is supervised *** learning has gained popular in recent *** could be used to address some emerging topics.

关键词： machine learning artificial intelligence finance

Subcritical dynamo and hysteresis in a Babcock-Leighton type kinematic dynamo model

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Research in Astronomy and Astrophysics 2021年第10期21卷 250-256页

作者： Vindya Vashishth Bidya Binay Karak leonid Kitchatinov Department of Physics Indian Institute of Technology(BHU)Varanasi 221005India Institute of Solar-Terrestrial Physics SB RAS Lermontov Str.126A664033IrkutskRussia Pulkovo Astronomical Observatory Pulkovskoe Sh.65St.Petersberg196140Russia

In the Sun and Sun-like stars,it is believed that cycles of the large-scale magnetic field are produced due to the existence of differential rotation and helicity in the plasma flows in their convection zones(CZs).Hence,it is expected that for each star,there is a critical dynamo number for the operation of a large-scale *** a star slows down,it is expected that the large-scale dynamo ceases to operate above a critical rotation *** our study,we explore the possibility of the operation of the dynamo in the subcritical region using the Babcock–Leighton type kinematic dynamo *** some parameter regimes,we find that the dynamo shows hysteresis behavior,i.e.,two dynamo solutions are possible depending on the initial parameters—decaying solution if starting with weak field and strong oscillatory solution(subcritical dynamo)when starting with a strong ***,under large fluctuations in the dynamo parameter,the subcritical dynamo mode is unstable in some parameter ***,our study supports the possible existence of subcritical dynamo in some stars which was previously demonstrated in a mean-field dynamo model with distributedαand MHD turbulent dynamo simulations.

关键词： magnetic field Sun:activity Sun:magnetic fields stars:rotation stars:dynamo stars

Ultrashort pulse laser ablation in liquids:probing the first nanoseconds of underwater phase explosion

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Light(Science & Applications) 2022年第6期11卷 1005-1007页

作者： Chaobo Chen leonid V.Zhigilei Department of Materials Science and Engineering University of Virginia395 McCormick RoadCharlottesvilleVA 22904-4745USA

The ultrafast pump-probe microscopy has shed new light on the complex dynamics of laser-induced explosive phase transformations and highlighted the importance of close integration of experimental,computational,and the... 详细信息

关键词： laser pump pulse