Intensity Oscillations Research Articles

INFLUENCE OF HELICAL CUTTING-EDGE ANGLE ON END-MILLING STABILITY

Increasing productivity, machining accuracy and efficient use of resources are important priorities for companies that manufacture competitive products. One of the main problems that hinders these processes is the vibration that occurs during cutting. Various methods are used to suppress vibration, one of which is the use of tools with a variable helical cutting-edge angle. However, when choosing the cutting-edge angle, it is important to consider the types of vibrations that occur during cutting, as they directly affect the efficiency of the milling process. In addition, the use of tools with different cutting-edge geometries, such as wavy, gives positive results in roughing, but becomes ineffective in finishing. The purpose of this paper is to study the effect of the helical cutting-edge angle on the stability of the end-milling at different cutting speeds. Both theoretical aspects and experimental data are considered, which make it possible to evaluate the effectiveness of using tools with different angles of inclination to ensure the stability of the machining process and increase productivity while minimizing vibrations in the most unfavorable third speed zone of oscillations for cutting. To conduct the experiments, a special stand was used to adjust the stiffness of the workpiece, record the vibrations that occur during cutting, and the time of contact between the workpiece and the tool. The milling was performed in the third high-speed oscillation zone using a tool whose design provides for the possibility of adjusting the angle of inclination of the helical cutting edge. Studies confirm that changing the angle of inclination can significantly affect the stability of the milling process, reducing the intensity of oscillations and improving machining accuracy. However, this effect depends on the initial cutting conditions, such as the cutting speed. With its increase, the amplitude of the accompanying free oscillations increases, regardless of the value of the angle of inclination. Ensuring the stability of the end-milling in the third speed zone by changing the angle of inclination is possible only at the speeds that determine the beginning of this zone. However, within the entire speed range covered by the third speed zone, it is impossible to ensure a stable milling process only due to the angle of inclination. The study emphasizes the importance of an integrated approach to selecting cutting parameters to achieve process stability.

A Python code for simulations of RHEED intensity oscillations within the one-dimensional dynamical approximation

A Python code for simulations of RHEED intensity oscillations within the one-dimensional dynamical approximation

Numerical Study of Supersonic Cavity Flows with Different Turbulent Models

A numerical study of supersonic cavity flows is conducted with different turbulent models, including RANS, LES, DES, DDES, and IDDES. Firstly, a supersonic cavity-ramp flow with Ma∞ = 2.92 is simulated numerically. It shows that the results of DDES and IDDES are nearly equivalent. The wall skin-friction coefficients obtained by these two models are in better agreement with the experimental measurement than those of DES. The reason is that the RANS region of DDES and IDDES is larger than that of DES, so it produces more turbulence in the near-wall region. In comparison, RANS cannot accurately predict large separation flows. The shear layer’s reattachment point on the ramp predicted by RANS is biased downstream compared to the experimental measurement, making its overall prediction accuracy worse than other models. The results obtained by LES are comparable to those obtained by DDES and IDDES except for the wall skin-friction coefficient, which is much smaller because the grid resolution is not high enough to accurately resolve the near-wall turbulent flow. Secondly, the effect of different aft-wall angles (θ) on the flow characteristics of the supersonic cavity is investigated numerically with IDDES. We find that as θ decreases, the oscillation intensity of the cavity flow continuously decreases. However, the change in cavity drag with θ is non-monotonic, which means that there might be a critical θ at which the drag penalties of a cavity are minimal. Therefore, an optimal design should be achieved when changing θ to control the oscillation intensity of supersonic cavity flows.

Specific heat analyses on optical-phonon-derived uniaxial negative thermal expansion system TrZr2 (Tr = Fe and Co1− xNix)

A large uniaxial negative thermal expansion (NTE) along the c-axis has recently been observed in the transition metal (Tr) zirconides TrZr2 with a tetragonal CuAl2-type structure. A recent study on FeZr₂ [M. Xu et al., Nat. Commun. 14, 4439 (2023)] suggests that optical phonons play a critical role in inducing the NTE along the c-axis. In this study, we investigate the thermophysical properties of TrZr₂ compounds (Tr = Fe and Co1− xNix(x = 0, 0.2, 0.4, 0.6, 0.8, 1)) using specific heat measurements, sound velocity data, and theoretical phonon calculations to achieve our aim of clarifying the contribution of optical phonons to the uniaxial NTE along the c-axis observed in both FeZr₂ and CoZr₂. We found that FeZr2 shows a lattice-specific heat peak structure at 8.90 meV, which corresponds to optical phonon energy with a high population of negative Grüneisen parameter along the c-axis in the phonon dispersion curves in FeZr2. In an examination of a chemical substitution effect on the Co1− xNixZr2, we found that the lattice-specific heat peak structure disappeared for x ≥ 0.4 and the oscillator intensity decreased. Phonon calculations revealed the existence of low-energy optical phonon branches at the Γ point for CoZr2 and FeZr2 with uniaxial NTE along the c-axis. However, the low-energy phonon branches were not found in NiZr2 with uniaxial positive thermal expansion along the c-axis. The increase in phonon density of states near the above optical phonon energy in CoZr2 and FeZr2 is consistent with the lattice-specific heat analyses, and we propose that low-energy optical phonons are essential for the exhibiting of uniaxial NTE along the c-axis in TrZr2.

Thread Displacement and Intensity Oscillations in a Quiescent Prominence

In this paper, we investigate the thread displacement and intensity oscillations in a quiescent prominence observed by New Vacuum Solar Telescope at the Hα line center on 2019 October 31. Each individual thread is traced by the local maximum intensity among its width at various times. In total, 35 threads are detected at six heights parallel to the solar surface. We find 29/35 threads exhibiting the displacement oscillation. A sinusoidal function is used to fit them, and a mean period of 26 minutes is identified. By slicing the same thread at different positions, we find that the oscillation of the thread is very likely a standing wave, but it could also be a long-wavelength propagating wave. After integrating the intensity along the thread width, we also find 8/35 threads presenting their intensity oscillation with a mean period of 7.7 minutes. In total, 7/35 threads exhibit both the displacement and the intensity oscillations.

Effect of injection distance on supersonic combustion under different combustion modes

The effect of injection distance on supersonic combustion under different modes in an ethylene-fueled scramjet combustor at Mach 2.52 is experimentally investigated. The study is based on three injectors at injection distances of 42, 21, and 7 mm. As the injection distance increases, a higher equivalence ratio is required to complete the transition from the Scram to Dual mode. The increase in injection distance will cause the reaction zone to move downstream in the Scram mode. However, the opposite is true in the Dual and Ram modes. In addition, the increase in injection distance will intensify the reaction zone oscillation under all modes. Moreover, in the Scram mode, shortening the injection distance will increase the heat release and the oscillation of heat release intensity. In the Dual mode, although shortening the injection distance cannot enhance the heat release, it will decrease the oscillation of heat release intensity. In the Ram mode, increasing the injection distance will enhance the heat release and will hardly increase the oscillation of heat release intensity. Considering the combustion heat release and oscillation, the injection distance should be shortened in the Scram and Dual modes and increased in the Ram mode.

Mesoscale eddy in situ observation and characterization via underwater glider and complex network theory.

Mesoscale eddies have attracted increased attention due to their central role in ocean energy and mass transport. The observations of their three-dimensional structure will facilitate the understanding of nonlinear eddy dynamics. In this paper, we propose a novel framework, the mesoscale eddy characterization from ordinal modalities recurrence networks method (MeC-OMRN), that utilizes a Petrel-II underwater glider for in situ observations and vertical structure characterization of a moving mesoscale eddy in the northern South China Sea. First, higher resolution continuous observation profile data collected throughout the traversal by the underwater glider are acquired and preprocessed. Subsequently, we analyze and compute these nonlinear data. To further amplify the hidden structural features of the mesoscale eddy, we construct ordinal modalities sequences rich in spatiotemporal characteristics based on the measured vertical density of the mesoscale eddy. Based on this, we employ ordinal modalities recurrence plots (OMRPs) to depict the vertical structure inside and outside the eddy, revealing significant differences in the OMRPs and the unevenness of density stratification within the eddy. To validate our intriguing findings from the perspective of complex network theory, we build the multivariate weighted ordinal modalities recurrence networks, through which network measures exhibit a more random distribution of vertical density stratification within the eddy, possibly due to more intense vertical convection and oscillations within the eddy's seawater micelles. These framework and intriguing findings are anticipated to be applied to more data-driven in situ observation tasks of oceanic phenomena.

Giant lateral shift in single mode cavity containing four-level sodium atomic medium

Abstract In this paper, a four-level sodium atomic medium coupled to a single-mode cavity is used to investigate the Goos-Ha¨nchen (GH) shift. Using the collective phase of the control fields and intensity of Rabi oscillation, the positive as well as negative GH-shift in transmission and reflection beams are examined. In the transmission beam, a maximum GH-shift of ±6λ is observed. Furthermore, GH-shift in both reflection and transmission beams in a four-level sodium atomic medium is significantly enhanced by photon number density as well as by the cavity coupling strength. By varying the collective phase of the control fields and the probe field frequency, GH-shift in reflection exhibits a maximum value of ±2λ. Our findings may open up significant applications in micro-optics, sensors, photonic crystals and nano-processor technology.

A method to enhance the performance of elastic damping component to improve tribological behavior at the high-speed train braking interface: Deformation optimization through perforation structure

The deformation capability of elastic damping component (EDC) significantly influences the tribological behavior at high-speed train braking interfaces. The key prerequisite to fully exploit its efficacy lies in ensuring that the EDC exhibits appropriate deformation. In this work, we propose aperture processing in different regions of the EDC to optimize its deformation area and improve the interfaces tribological behavior. The EDC was mounted on the rear side of the friction block, and experiments on friction braking were carried out using a custom-built simulation rig designed to test the braking performance. This enables the study of the friction and wear characteristics across different EDC conditions, along with the characteristics related to friction-induced vibration and noise (FIVN). A finite element model (FEM) was developed reflecting the primary structure of the test rig, with initial surface wear simulations conducted on the blocks to achieve wear surfaces approximating the experimental outcomes. Implicit dynamic analysis (IDA) was then conducted based on this foundation. The enhancement in tribological behavior through optimizing the EDC deformation area was analyzed by integrating test results with finite element analysis (FEA) findings. The results indicate that aperture processing in different regions of the EDC has no significant effect on its dynamic response but can significantly alter its deformation characteristics, thereby achieving optimization of the EDC deformation. Adjusting apertures in various sections of the EDC markedly affects the development pattern and strength of FIVN. However, this approach maintains the fundamental characteristics of the braking system. Aperture processing enabling more extensive deformation in the EDC can notably interrupt FIVN continuity, showing clear intermittent characteristics, while potentially increasing FIVN intensity. The EDC mainly affects the tribological behavior by influencing contact characteristics such as the oscillation intensity of contact area and frictional force, thereby altering the characteristics of FIVN. The overall deformation of the EDC has a considerable effect on the movement of braking interface debris, as well as wear patterns, eccentric wear, and contact plateaus characteristics. An improperly designed deformation area in the EDC can lead to excessive softness, challenging the block's ability to maintain consistent contact with the brake disc. This issue often causes pronounced eccentric wear on the block and considerable material detachment at the wear site, which triggers intense FIVN.

Phonon-Coupled High-Harmonic Generation for Exploring Nonadiabatic Electron-Phonon Interactions.

High harmonic generation (HHG) have received significant attention for the exploration of material properties and ultrafast dynamics. However, the lack of consideration for couplings between HHG and other quasiparticles, such as phonons, has been impeding the understanding of many-body interactions in HHG. Here, we reveal the many-body electron-phonon mechanism in the quasiparticle-coupled strong-field dynamics by investigating the nonadiabatic (NA) coherent-phonon-coupled HHG. Coherent phonons are revealed to effectively affect HHG via the adiabatic band modulation induced by phonon deformation effects and the NA and nonequilibrium distribution of photocarriers in multiple valleys. The adiabatic and NA mechanisms leave their fingerprint via influencing the phonon period and phase delay in the oscillation of HHG intensity, both of which are experimentally measurable. Investigation of these quantities enables the direct probing of the electron-phonon interaction in materials.

Experimental Study on Pressure Oscillation Characteristics of Di-N-Butyl Ether in a Constant Volume Vessel

ABSTRACT This paper conducted experimental research on spontaneous pressure oscillation characteristics of di-n-butyl ether (DBE). Based on a constant volume vessel (CVV) with 210 mm in length and 180 mm in diameter, the initial pressure, temperature, and equivalence ratio ranges of 0.05–0.3 MPa, 373–453 K, and 0.7–1.6. The experimental data of combustion pressure, CVV vibration and sound pressure were analyzed. The results indicate that DBE exhibits the strongest pressure oscillation at high pressures, moderate temperatures and equivalence ratios. The highest oscillation intensity is achieved at 0.3 MPa, 433 K, equivalence ratio of 1.4. The vibration and sound pressure signals exhibit the same patterns as combustion pressure signals. Spectrum analysis is conducted by Fast Fourier Transform of pressure signals, it shows that the amplitude of the characteristic frequency increases with the increase of oscillation intensity. In addition, to further reveal the influence of combustion instability on oscillation intensity, the dimensionless parameter Peclet number and critical radius are compared, it shows that the combustion instability has strong effect on pressure oscillation, and diffusive-thermal instability is the key factor that influences pressure oscillation. This study is believed to be beneficial for organizing better combustion for internal combustion engines.

Observation of Standing Slow Magneto-acoustic Waves in a Flaring Active Region Corona Loop

Intensity fluctuations are frequently observed in different regions and structures of the solar corona. These fluctuations may be caused by magneto-hydrodynamic (MHD) waves in coronal plasma. MHD waves are prime candidates for the dynamics, energy transfer, and anomalous temperature of the solar corona. In this paper, analysis is conducted on intensity and temperature fluctuations along the active region coronal loop (NOAA AR 13599) near solar flares. The intensity and temperature as functions of time and distance along the loop are extracted using images captured by the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) space telescope. To observe and comprehend the causes of intensity and temperature fluctuations, after conducting initial processing, and applying spatial and temporal frequency filters to data, enhanced distance-time maps of these variables are drawn. The space-time maps of intensities show standing oscillations at wavelengths of 171, 193, and 211 Å with greater precision and clarity than earlier findings. The amplitude of these standing oscillations (waves) decreases and increases over time. The average values of the oscillation period, damping time, damping quality, projected wavelength, and projected phase speed of standing intensity oscillations are in the range of 15–18 minutes, 24–31 minutes, 1.46″–2″, 132″–134″, and 81–100 km s−1, respectively. Also, the differential emission measure peak temperature values along the loop are found in the range of 0.51–3.98 MK, using six AIA passbands, including 94, 131, 171, 193, 211, and 335 Å. Based on the values of oscillation periods, phase speeds, damping time, and damping quality, it is inferred that the fluctuations in intensity are related to standing slow magneto-acoustic waves with weak damping.

Investigating high-frequency quasi-periodic oscillations in the 6374 Å red coronal line observed during the total solar eclipse on August 21, 2017

Context. We present the results of the search for high-frequency quasi-periodic oscillations (HFQPOs) in the 6374-Å red line emission from the solar corona during the 2017 total solar eclipse (TSE). Aims. The existence of HFQPOs of coronal intensity remains unclear. Motivated by previous observations, this paper focuses on searching for the HFQPOs (> 0.1 Hz) during the 2017 TSE. Methods. Wavelet analysis tools were used to analyze the radiation intensity oscillations in different height layers, local regions of interest (such as the east coronal loop, west cavity, etc.), and coronal feature points as well as changes in oscillations along coronal feature structures and the kinematic wobble of the coronal magnetic features. Results. We have observed oscillatory signals at multiple spatial locations, which reveal the existence of quasi-periodic slow magnetoacoustic waves. These signals display periods ranging from approximately 3 to 9 seconds, with a notable focus on periods around 4 seconds. Conclusions. High-frequency quasi-periodic slow magnetoacoustic oscillations (with periods less than 9.63 seconds) have been identified in the inner corona (at heights less than 1.4 R⊙) in the 6374 Å red coronal line radiation.

Modeling of the separation process of a two-phase liquid in a high-temperature gas environment

Obtaining a high-quality highly dispersed salt solution can be realized from a salt solution by the method of ultrasonic exposure. As you know, concentrated salt solutions can be presented in the form of a gas-liquid medium. The influence of ultrasound, in the case of wetting a surface vibrating with an ultrasonic frequency by a thin layer, leads to the formation of a cavitation layer in the liquid layer and capillary waves on its surface, from the ridges of which, at a certain intensity of oscillations, finely dispersed aerosol droplets are detached.The detachment of droplets from the vibrating surface leads to the formation of finely dispersed salt aerosol, which saturates the heated air, which is tangentially fed into the cylindrical working chamber with further separation of hydrodynamic processes. Part of the aerosol wets the heated inner surface of the cylindrical chamber with the formation of a thin film, which gravitationally flows down the vertical solid surface and is subjected to active evaporation with the removal of the salt phase, and the second part is subjected to additional grinding and active evaporation in the central turbulent flow and centrifugal turbulent flow of hot air with additional by removing the salt phase. In order to intensify the salt removal process, the surface on which the film is formed can be profiled. Ultrasonic dispersion of the salt solution to a finely dispersed state allows to significantly increase the surface of contact with the heated air, which allows to intensify the diffusion process.

Enhanced mixing characteristics of unbaffled U-shaped microreactor coupled oscillatory flow

The Microscale Oscillatory Flow Reactor (MOFR) can achieve good plug flow and micromixing performance simultaneously at laminar net flow conditions. An unbaffled U-shaped microreactor coupled with oscillating flow technology was designed to study the macro and micromixing performance. Firstly, the influence of oscillations on the flow performance was studied to reveal the formation rule of vortex. The simulation results showed that the continuous formation and destruction of periodic vortexes occurred in the microreactor with oscillation. With the increase of oscillation intensity, the vortex size in the radial direction first gradually increased and then becomes stable, and gradually moved axially, resulting in axial diffusion. Secondly, the effect of oscillation on the macromixing and micromixing performance were investigated. The results showed that the coupling oscillation could greatly improve the macromixing and micromixing performance. The macromixing and micromixing performance were promoted simultaneously at lower oscillation intensity and then tended to be flat due to the axial diffusion at high oscillation intensity. When φ>6.05, the minimum micromixing time and the maximum number of tanks can be achieved at the same time. At a velocity ratio of about 23, FoM reached a maximum of about 3.5.

Novel insights into photoaging mechanisms and environmental persistence risks of polylactic acid (PLA) microplastics: Direct and indirect photolysis

Polylactic acid (PLA), as a biodegradable plastic, exhibits high sensitivity to ultraviolet (UV) radiation, yet the mechanisms and environmental risks of its photoaging remain unclear. This study uses quantum chemical calculations (DFT and TD-DFT) and kinetic simulations to explore the direct and indirect photoaging of PLA. Direct photoaging indicates that the highest oscillator intensity absorption peaks occurred at 172 and 246 nm, corresponding to the 13th singlet (S13) and 48th triplet (T48) states, thereby initiating the Norrish I and Norrish II mechanisms. The innovative “electron-hole” technology effectively clarifies the variations in photoaging mechanisms under different wavelengths. Indirect photoaging involves multiple reactive oxygen species (ROS) like •OH, 1O2, •O2−, and •HO2. The study confirms the anhydride production hypothesis and proposes two novel •OH-induced mechanisms: carbonyl carbon addition and branched methyl hydrogen dehydrogenation. Both mechanisms are thermodynamically advantageous, but their products pose potential environmental risks. ROS species and concentrations impact both PLA's photoaging mechanisms and environmental persistence. Low •OH concentration in northeast China, especially in winter, suggests a significant photoaging risk. This study offers pioneering insights into photoaging mechanisms and emphasizes the pivotal role of ROS, offering recommendations for managing PLA environmental impacts and fates in China.

A search for mode coupling in magnetic bright points

Magnetic bright points (MBPs) are one of the smallest manifestations of the magnetic field in the solar atmosphere and are observed to extend from the photosphere up to the chromosphere. As such, they represent an excellent feature to use in searches for types of magnetohydrodynamic (MHD) waves and mode coupling in the solar atmosphere. In this work, we aim to study wave propagation in the lower solar atmosphere by comparing intensity oscillations in the photosphere with the chromosphere via a search for possible mode coupling, in order to establish the importance of these types of waves in the solar atmosphere, and their contribution to heating the chromosphere. These observations were conducted in July 2011 with the Rapid Oscillations of the Solar Atmosphere (ROSA) and the Hydrogen-Alpha Rapid Dynamics Camera (HARDCam) instruments at the Dunn Solar Telescope. Observations with good seeing were made in the G-band and Halpha wave bands. Speckle reconstruction and several post facto techniques were applied to return science-ready images. The spatial sampling of the images was 0.069arcsec /pixel (50 km/pixel). We used wavelet analysis to identify traveling MHD waves and derive frequencies in the different bandpasses. We isolated a large sample of MBPs using an automated tracking algorithm throughout our observations. Two dozen of the brightest MBPs were selected from the sample for further study. We find oscillations in the G-band MBPs, with frequencies between 1.5 and 3.6 mHz. Corresponding MBPs in the lower solar chromosphere observed in Halpha show a frequency range of 1.4 to 4.3 mHz. In about 38<!PCT!> of the MBPs, the ratio of Halpha to G-band frequencies was near two. Thus, these oscillations show a form of mode coupling where the transverse waves in the photosphere are converted into longitudinal waves in the chromosphere. The phases of the Halpha and G-band light curves show strong positive and negative correlations only 21<!PCT!> and 12<!PCT!> of the time, respectively. From simple estimates we find an energy flux of approx 45 $ $ W m$^ $ and show that the energy flowing through MBPs is enough to heat the chromosphere, although higher-resolution data are needed to explore this contribution further. Regardless, mode coupling is important in helping us understand the types of MHD waves in the lower solar atmosphere and the overall energy budget.

Vortex-Induced Vibration (VIV) of flexible riser conveying severe slugging and straight flow in steady and oscillatory flows

This paper aims to investigate dynamic characteristics of Vortex-Induced Vibration (VIV) of a flexible riser conveying severe slug flow and straight flow in steady and oscillatory flows. Firstly, a classical wake oscillator model is adopted to simulate the coupling effects between internal and external flows on dynamic characteristics of VIV and an improved wake oscillator model is developed to calculate responses of VIV in oscillatory flow. A two-dimensional (2D) Computational Fluid Dynamics (CFD) model is developed to predict the behavior of severe slug flow. Then, structural equations of riser are discretized by adopting central difference method, and the Runge-Kuta method is adopted to solve them and the wake oscillator equations. The results show that characteristics of VIV, including root mean square (RMS) of displacement, dominant modes and vibration frequencies of riser conveying severe slugging differ significantly from those of riser conveying straight flow. New mode responses are triggered and multi-frequency phenomenon is observed due to severe slug flow. In addition, responses of VIV of riser conveying severe slug flow are influenced by the variation of the velocity or oscillation intensity of external flow. Model transition is normally triggered with a high-velocity sheared flow or a high Keulegan-Carpenter (KC) number.

Spatio‐Temporal Characteristics and Variability of GNSS‐Derived Atmospheric Precipitable Water Vapor From 2010 to 2023 in Fujian Province, China

AbstractAtmospheric precipitable water vapor (PWV) is a crucial factor affecting precipitation and the atmospheric environment. To quantitatively investigate the spatio‐temporal distribution and characteristics of the PWV in Fujian, China, its diurnal and seasonal variations are analyzed based on the global navigation satellite system (GNSS) data from 2010 to 2023, ground meteorological observations, meteorological sounding data and ERA5 data. Moreover, the spatio‐temporal characteristics of the monthly PWV are assessed by using the empirical orthogonal function (EOF), the Mann‐Kendall test and the sliding t‐test. The results indicate that the ground‐based GNSS PWV data is able to reveal the distribution and variation of PWV over Fujian. Specifically, the diurnal distribution of the PWV varies remarkably with time, and the PWV in the eastern coastal areas is generally higher than in the western mountainous areas. The seasonal variation characteristics of the PWV are consistent with the atmospheric circulation variations, with the largest amount of PWV in summer, followed by spring, autumn and winter. Moreover, the EOF spatial modes show that the PWV distributions are different in the eastern coastal areas and inland mountainous areas. The oscillation intensity of the PWV strengthens from the northwest to the southeast, and the corresponding time series of the PWV displays apparent seasonal variations. The observed precipitation is inconsistent with the PWV and is more affected by local terrain and thermodynamic conditions. The Mann‐Kendall test and the sliding t‐test indicate that the PWV over Fujian has not undergone abrupt changes during the past 13 years, but there is a possibility of sudden changes in the future.

Quasiperiodic Oscillations of Flare Loops and Slipping Motion of Ribbon Substructures during a C-class Flare

Quasiperiodic oscillations in solar-flaring emission have been observed over the past few decades. To date, the underpinning processes resulting in the quasiperiodic oscillations remain unknown. In this paper, we report a unique event that exhibits both the long-duration quasiperiodic intensity oscillations of flare loops and the quasiperiodic slipping motion of ribbon substructures during a C9.1-class flare (SOL2015-03-15-T01:15), using the observations from the Solar Dynamics Observatory and Interface Region Imaging Spectrograph. The high-temperature flare loops rooted in the straight part of ribbons display a “bright–dim” intensity oscillation, with a period of about 4.5 minutes. The oscillation starts just after the flare onset and lasts over 3 hr. Meanwhile, the substructures within the ribbon tip display the quasiperiodic slipping motion along the ribbon at 1400 Å images, which has a similar periodicity to the stationary intensity oscillation of the flare loops in the straight part of the flare ribbons. We suggest that the quasiperiodic pattern is probably related to the loop-top dynamics caused by the reconnection outflow impinging on the flare loops.