Periodic Variations Research Articles

Numerical modelling of the interaction between dialysis catheter, vascular vessel and blood considering elastic structural deformation.

The dialysis catheter indwelling in human bodies has a high risk of inducing thrombus and stenosis. Biomechanical research showed that such physiological complications are triggered by the wall shear stress of the vascular vessel. This study aimed to assess the impact of CVC implantation on central venous haemodynamics and the potential alterations in the haemodynamic environment related to thrombus development. The SVC structure was built from the images from computed tomography. The blood flow was calculated using the Carreau model, and the fluid domain was determined by CFD. The vascular wall and the CVC were computed using FEA. The elastic interaction between the vessel wall and the flow field was considered using FSI simulation. With consideration of the effect of coupling, it was shown that the catheter vibrated in the vascular systems due to the periodic variation of blood pressure, with an amplitude of up to 10% of the vessel width. Spiral flow was observed along the catheter after CVC indwelling, and recirculation flow appeared near the catheter tip. High OSI and WSS regions occurred at the catheter tip and the vascular junction. The arterial lumen tip had a larger effect on the WSS and OSI values on the vascular wall. Considering FSI simulation, the movement of the catheter inside the blood flow was simulated in the deformable vessel. After CVC indwelling, spiral flow and recirculation flow were observed near the regions with high WSS and OSI values.

Stellar Cycle and Evolution of Polar Spots in an M+WD Binary

Stellar activity cycles reveal continuous relaxation and induction of magnetic fields. The activity cycle is typically traced through the observation of cyclic variations in total brightness or Ca H&K emission flux of stars, as well as cyclic variations in the orbital periods of binary systems. In this work, we report the identification of a semidetached binary system (TIC 16320250) consisting of a white dwarf (0.67 M ⊙) and an active M dwarf (0.56 M ⊙). The long-term multiband optical light curves spanning twenty years revealed three repeated patterns, suggestive of a possible activity cycle of about 10 years of the M dwarf. Light-curve fitting indicates the repeated variation is caused by the evolution, particularly the motion, of polar spots. The significant Ca H&K, Hα, ultra-violet, and X-ray emissions imply that the M dwarf is one of the most magnetically active stars. We propose that in the era of large time-domain photometric sky surveys (e.g., ASAS-SN, Zwicky Transient Facility, LSST, Sitian), long-term light-curve modeling can be a valuable tool for tracing and revealing stellar activity cycle, especially for stars in binary systems.

The nature of medium-period variables on the extreme horizontal branch

A fraction of the extreme horizontal branch stars of globular clusters exhibit a periodic light variability that has been attributed to rotational modulation caused by surface spots. These spots are believed to be connected to inhomogeneous surface distribution of elements. However, the presence of such spots has not been tested against spectroscopic data. We analyzed the phase-resolved ESO X-shooter spectroscopy of three extreme horizontal branch stars that are members of the globular cluster ω Cen and also display periodic light variations. The aim of our study is to understand the nature of the light variability of these stars and to test whether the spots can reproduce the observed variability. Our spectroscopic analysis of these stars did not detect any phase-locked abundance variations that are able to reproduce the light variability. Instead, we revealed the phase variability of effective temperature and surface gravity. In particular, the stars show the highest temperature around the light maximum. This points to pulsations as a possible cause of the observed spectroscopic and photometric variations. However, such an interpretation is in a strong conflict with Ritter’s law, which relates the pulsational period to the mean stellar density. The location of the ω Cen variable extreme horizontal branch stars in HR diagram corresponds to an extension of PG 1716 stars toward lower temperatures or blue, low-gravity, large-amplitude pulsators toward lower luminosities, albeit with much longer periods. Other models of light variability, namely, related to temperature spots, should also be tested further. The estimated masses of these stars in the range of 0.2–0.3 M⊙ are too low for helium-burning objects.

Effects of the structural period variations and near field earthquakes on a fuzzy controller performance for the variably baffled tuned liquid damper

Effects of the structural period variations and near field earthquakes on a fuzzy controller performance for the variably baffled tuned liquid damper

Monitoring long‐term vegetation dynamics over the Yangtze River Basin, China, using multi‐temporal remote sensing data

AbstractVegetation plays a crucial role in nature, with intricate interactions between it and the geographical environment. The Yangtze River Basin (YRB) refers to the third largest river basin globally and an essential ecological security barrier in China. Monitoring vegetation dynamics in the basin is of profound significance for addressing climate change, soil erosion, and biodiversity loss in the basin's ecosystems. Here, we investigate the spatiotemporal variations of vegetation at both the basin and land cover scales in the YRB from 2000 to 2020. We elucidate the determinants driving the changes and explore future normalized difference vegetation index (NDVI) trends. The results indicate that NDVI in the YRB increased at a rate of 0.0032 year−1 (p < 0.01) over the past 21 years, and it is anticipated to maintain an upward trend in the future. Regions in the upper and middle reaches of the YRB demonstrated higher NDVI, whereas regions in the headwater area and the lower reaches showed lower NDVI. Significant vegetation improvement was primarily concentrated in the central part of the basin, while noticeable vegetation degradation was observed in the eastern region. Temperature and wind speed were identified as the primary controlling factors affecting vegetation greenness. Global‐scale climate oscillations played a significant role in driving periodic variations in NDVI, with La Niña events tending to increase NDVI, while El Niño events hindered its rise. Land cover types were influenced by long‐term interactions between natural factors and human activities, although short‐term vegetation variations might be more affected by the latter. Our findings provide valuable insights into the mechanisms behind vegetation variability driven by multiple variables, and the strong vegetation carbon sink capacity advances the conservation and development of ecosystems.

Unveiling hidden companions in post-common-envelope binaries: A robust strategy and uncertainty exploration

Context. Some post-common-envelope binaries (PCEBs) are binary stars with short periods that exhibit significant period variations over long observational time spans. These eclipse timing variations (ETVs) are most likely to be accounted for by the presence of an unseen massive companion, potentially of planetary or substellar nature, and the light-travel time (LTT) effect. The existence of such companions challenges our current understanding of planetary formation and stellar evolution. Aims. In this study, our main objective is to describe the diversity of compatible nontransit companions around PCEBs and explore the robustness of the solutions by employing tools for uncertainty estimation. We select the controversial data of the QS Vir binary star, which previous studies have suggested hosts a planet. Methods. We employ a minimizing strategy, using genetic algorithms to explore the global parameter space followed by refinement of the solution using the simplex method. We evaluate errors through the classical Markov chain Monte Carlo (MCMC) approach and discuss the error range for parameters, considering the 1σ values obtained from the minimization. Results. Our results highlight the strong dependence of ETV models for close binaries on the dataset used, which leads to relatively loose constraints on the parameters of the unseen companion. We find that the shape of the O – C curve is influenced by the dataset employed. We propose an alternative method to evaluate errors on the orbital fits based on a grid search surrounding the best-fit values, obtaining a wider range of plausible solutions that are compatible with goodness-of-fit statistics. We also analyze how the parameter solutions are affected by the choice of the dataset, and find that this system continuously changes the compatible solutions as new data are obtained from eclipses. Conclusions. The best-fit parameters for QS Vir correspond to a low-mass stellar companion (57.71 Mjup ranging from ~40 to ~64 Mjup) on an eccentric orbit (e = 0.91−0.17+0.07) with a variety of potential periods (P = 16.69−0.42+0.47 yr.). Most solutions within 1σ exhibit regular orbits, despite their high eccentricity. Additional observations are required to accurately determine the period and other parameters of the unseen companion. In this context, we propose that a fourth body should not be modeled to fit the data, unless new observations considerably modify the computed orbital parameters. This methodology can be applied to other evolved binary stars suspected of hosting companions.

Research and Application of Coal Seam Permeability Improvement Technology by Sectional Directional Hydraulic Fracturing

To address the challenging issue of gas control in the working faces of the Hegang mining area, based on segmented directional hydraulic fracturing technology, ABAQUS simulation software was employed to simulate and analyze the fracturing process of coal-rock masses under the action of segmented hydraulic fracturing. The study focused on the engineering application research within the mining roadway of the 23# coal seam in the Junde Coal Mine, China. The results indicate that the numerical simulation analysis reveals elliptical patterns in the stress, strain, and fracture width variation of the coal-rock masses influenced by the fracturing action. The width of the fractures exhibits a periodic variation pattern, initially increasing and then slightly decreasing with the injection of water pressure. Additionally, each successive variation shows a decreasing magnitude. After applying segmented hydraulic fracturing technology, the average gas extraction concentration increased by a maximum of 1.73 times, the average mixed flow rate increased by a maximum of 2.16 times, and the average gas extraction pure quantity increased by a maximum of 3.10 times. Segmented hydraulic fracturing can effectively improve gas extraction efficiency, reduce coal seam gas content, and have a depressurizing effect on coal-rock layers. The research findings provide new means for safe and efficient coal mining, particularly in enhancing gas extraction efficiency, alleviating strata pressure, and preventing gas disasters.

Periodic Behavior of Selected Solar, Geomagnetic and Cosmic Activity Indices during Solar Cycle 24

In this study, we performed periodicity analyses of selected daily solar (flare index, coronal index, number of coronal mass ejections), geomagnetic (planetary equivalent range index, disturbance storm time index, interplanetary magnetic field) and cosmic ray indices for the last Solar Cycle 24 (from December 2008 to December 2019). To study the periodic variation of the above-listed datasets, the following analysis methods were applied; multi-taper method, Morlet wavelet, cross-wavelet transform and wavelet coherence analysis. The outcome of our analyses revealed the following. (i) The 25–33 days solar rotation periodicities exist in all datasets without any exception in the MTM power spectra. (ii) Except for the solar rotation periodicity, all periods show data preference, and they appear around the investigated cycle’s maximum phase. (iii) When comparing the phase relations between periodicities in the used datasets, they exhibit a gradual transition from small to large periods. For short-term periodicities, there are no phase relations but a mixed phase, whereas for high periodicities, there are complete phase/antiphase transitions. (iv) All identified flare index periodicities are common to all other datasets examined in this investigation.

Variation in the Reflection Height of VLF/LF Transmitter Signals in the D‐Region Ionosphere and the Possible Source: A 2018 Meteoroid in Hokkaido, Japan

AbstractSeveral studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D‐region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D‐region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low‐frequency (VLF, 3–30 kHz) and low‐frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi‐net and F‐net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D‐region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi‐net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D‐region height (about ∼90 km altitude), south of the Rikubetsu receiver.

Numerical study on dust particle charging and dynamics in continuous and pulsed radio frequency argon discharges

AbstractCharging and dynamics of a spherical dust grain injected into a continuous and pulsed radio frequency (RF) discharge have been studied using a one‐dimensional fluid model. First, the plasma characteristics of the two types of discharges are computed and compared. In the pulsed discharge, it is found that the central electron density exhibits a periodic variation while the averaged electron density is lower compared to that in the continuous discharge due to the decrease in the total ionization rate. Further, the dust charge is computed using the plasma characteristics. It is found that the dust charge negatively increases as the duty cycle ratio increases. Also, the charge in the pulsed discharge is lower in comparison to the continuous discharge due to the shorter duration of the pulsed RF discharge limiting the amount of energy transferred to electrons. On the other hand, the dust particle remains in the powered sheath region exhibiting a damped oscillation in the two discharges with higher oscillation frequency in the continuous discharge.

Statistical analysis of disability-adjusted life years for stomach and colorectal cancers in Changning District of Shanghai

Objectives: To analyze the status and temporal changes of disability-adjusted life year (DALY) for stomach and colorectal cancers among registered permanent residents in Changning District of Shanghai Municipality, and provide scientific basis for the prevention and treatment of stomach and colorectal cancers in this district. Methods: Using the cancer registration data of stomach and colorectal cancers from 2002 to 2019, we estimated the indices such as the DALYs, the DALY crude rates, the age-standardized DALY rates, etc. Then we used the Joinpoint regression model to calculate the average annual percent change (AAPC) and annual percent change (APC) to explore the temporal variations in different periods. Results: The DALYs of stomach and colorectal cancers in Changning District from 2002 to 2019 were 55 931 person years and 65 252 person years, respectively. The crude rates of DALY were 512.16/105 and 597.51/105, respectively. We observed a higher disease burden in men than in women, and the peak rate of DALY in stomach cancer was in the 75-79 years age group, while in colorectal cancer the rate was in the 85-years-or-older age group. Joinpoint regression analysis showed that from 2002 to 2019, the age-standardized DALY rate of stomach cancer showed a downward trend (AAPC=-3.86%, P＜0.05), while the trend of colorectal cancer was not statistically significant(AAPC=-0.08%, P＞0.05). However, the trends in the age-standardized DALY rates of colorectal cancer were different between males and females, with males showing an upward trend (AAPC=1.24%, P＜0.05) and females showing a downward trend (AAPC=-1.67%, P＜0.05). Conclusions: The DALY of stomach and colorectal cancers in Changning District of Shanghai showed a decreasing trend. Males and the middle-aged and elderly populations are still the key targets for disease prevention and control in this district.

Rapid polarization variations in the O4 supergiant ζ Puppis

ABSTRACT We present time-series linear-polarization observations of the bright O4 supergiant ζ Puppis. The star is found to show polarization variation on time-scales of around an hour and longer. Many of the observations were obtained contemporaneously with Transiting Exoplanet Survey Satellite (TESS) photometry. We find that the polarization varies on similar time-scales to those seen in the TESS light curve. The previously reported 1.78-d photometric periodicity is seen in both the TESS and polarization data. The amplitude ratio of photometry to polarization is ∼9 for the periodic component and the polarization variation is oriented along position angle ∼70°–160°. Higher frequency stochastic variability is also seen in both data sets with an amplitude ratio of ∼19 and no preferred direction. We model the polarization expected for a rotating star with bright photospheric spots and find that models that fit the photometric variation produce too little polarization variation to explain the observations. We suggest that the variable polarization is more likely the result of scattering from the wind, with corotating interaction regions producing the periodic variation and a clumpy outflow producing the stochastic component. The Hα emission line strength was seen to increase by 10 per cent in 2021 with subsequent observations showing a return to the pre-2018 level.

Periodic transmission theory of circularly symmetric multi-ring solitons in nonlinear Schrödinger equation

In this paper, the evolution characteristics of periodic transmission of circularly symmetric multi-ring solitons in optical nonlocal materials based on nonlinear Schrödinger equation are investigated in detail. The transmission expression of circularly symmetric multi-ring solitons has been derived. It was found that the number and size of rings in these solitons can be controlled by initial parameters. The transmission of circularly symmetric multi-ring solitons is similar to that of high-order temporal solitons in nonlinear fibers, exhibiting periodic variations. When the input energy is a specific value, the statistical width of circularly symmetric multi-ring solitons remains constant during transmission, otherwise it exhibits periodic changes, which can be considered as generalized breathing solitons. The influence of various parameters on the transmission characteristics has been analyzed in detail, and some important transmission characteristics have been intuitively demonstrated through numerical simulation.

Hydrodynamic models of pulsation period evolution in R Hydrae

ABSTRACT Pulsation period evolution during the helium–shell flash in the Mira variable R Hya is investigated using consistent stellar evolution and non-linear stellar pulsation computations. The initial and time-dependent inner boundary conditions for the equations of radiation hydrodynamics describing non-linear stellar oscillations were determined using a grid of TP–AGB model sequences with initial masses on the main sequence 1.5M⊙ ≤ MZAMS ≤ 5.0M⊙ and the initial metallicity Z = 0.014. The setup of initial conditions for hydrodynamic models corresponds to ≈100 yr prior to the maximum of the helium–shell luminosity and ensures that the stellar envelope of the evolution model is under both hydrostatic and thermal equilibrium. Solution of the equations of hydrodynamics allowed us to determine the temporal variation of the pulsation period Π(t) during ≈500 yr. Within this time interval R Hya is a fundamental mode pulsator. The period temporal dependencies Π(t) calculated for the AGB star models at the beginning of the third dredge-up phase and with masses $4.4M_{\odot }\lessapprox M\lessapprox 4.5M_{\odot }$ are in agreement with observational estimates of the period of R Hya obtained during last two centuries. The mean radius of R Hya pulsation models at the end of the XX century ($470 R_{\odot }\lessapprox \bar{R}\lessapprox 490 R_{\odot }$) agrees with observational estimates obtained using the interferometric angular diameter measurements.

Propagation dynamics of self-accelerating second-order Hermite complex-variable-function Gaussian wave packets in a harmonic potential

This paper investigates the evolutionary dynamics of self-accelerating second-order Hermite complex-variable-function Gaussian (SSHCG) wave packets in a harmonic potential. The periodic variation of the wave packets is discussed via theoretical analysis and numerical simulation. The control variables method is applied to manipulate the distribution factor, cross-phase factor, potential depth, and chirp parameter, enabling the realization of unique propagation dynamics. In three-dimensional models, the SSHCG wave packets exhibit rotational states, featuring butterfly shape, three peaks shape, two polarity shape, elliptical shape, and ring-shaped double-vortex structures. Furthermore, the energy flow and the angular momentum of the wave packets are investigated. Additionally, the performance of the radiation force on a Rayleigh dielectric particle is studied. This investigation results in the emergence of distinct SSHCG wave packet propagation dynamics, and potential applications in optical communications and optical trapping are presented.

Numerical simulation study on the effect of internal heat source on pumping ventilation

Natural ventilation is a passive building technology that can reduce energy consumption for mechanical cooling of the indoor environment. Natural ventilation technology has received renewed attention from researchers. Theoretical studies on natural ventilation have evolved from a steady state to a non-steady state. Pumping ventilation is distinct from other ways of natural ventilation in that its flow direction alternatingly changes from the indoor to the outdoor. However, all published studies did not consider the influence of internal heat sources in pumping ventilation, and there are few discussions about the fluid periodic variation in wind-thermal coupling studies. Based on a previous study, the numerical simulation of single-sided pumping ventilation with two openings in the same wall driven by wind and thermal pressure is conducted in the paper. The influence of heat source intensity and the height of the location of the heat source are analyzed. The applicability of different ventilation rate calculation formulas is discussed. The results show that the indoor airflow oscillation frequency decreases in the effect of wind and thermal pressure, compared to driven by air pressure alone. However, changing the height location and intensity of the heat source does not affect the frequency characteristics in these cases.

In-situ synthesis of high-performance TiN/TC4 sandwich structures via nitrogen-controlled laser directed energy deposition

Laser Directed Energy Deposition (LDED) additive manufacturing offers a versatile approach for fabricating composite materials, encompassing a wide range of heterogeneous and transition materials, known for their exceptional mechanical properties. In this study, we focus on the synthesis of TiN/TC4 sandwich structural materials in atmospheres characterized by varying nitrogen-to-argon ratios. This study includes the in-situ synthesis, microstructural evolution, and mechanical characteristics of these TiN/TC4 sandwich structures during the LDED process. Through this process, TiN was formed in-situ by the interaction of Ti and N atoms, exhibiting in robust metallurgical bonding with the TC4 matrix. Notably, the microhardness of the TiN/TC4 sandwich structures exhibits periodic variations along the deposition direction, ranging between 314.4 HV0.2 and 661.5 HV0.2. The tensile strength of the TiN/TC4 sandwich structures experiences significant enhancement, while maintaining toughness due to the laminate structure and reinforced with ceramic particles inside. The resulting sandwich composites demonstrate outstanding ultimate tensile strength, which can achieve 1123.3 ± 29.7 MPa. This represents a notable improvement of 20.3% over the TC4 deposited in a pure Ar environment, with a corresponding plastic strain of 2.5 ± 1.7%. This study demonstrates that layered heterogeneous materials with superior mechanical strength can be synthesized in-situ through flexible integration of LDED process and reaction atmospheres.

Sensing analysis of self-mixing and Michelson interferometry with neural-network-based phase extraction

Self-mixing interference (SMI) and Michelson interference (MI) with the phase extraction method based on a neural network (NN) for sensing is analyzed in this work. Since MI and SMI signals are predominantly a cosine-like function of optical phase, the NN’s core task involves mapping the cosine function to phase values, which is solved by a tectonic characteristic function. Experimental results show that the movement information carried by MI and SMI signals can be accurately measured by the NN with a phase sensitivity of 10−3 rad, yielding outcomes that align with the simulations. Especially, algorithms are essential for extracting real-time motion direction of objects in MI. The simplicity of real-time motion direction extraction is the key advantage of SMI, while further utilization of variational mode decomposition is necessary to mitigate the impact of periodic optical frequency variation. This work offers a potentially valuable contribution to develop interferometry for engineering applications.

A dynamic view of V Hydrae

Context. The well studied carbon star V Hydrae is known to exhibit a complex asymmetric environment made of a dense equatorial wind and high-velocity outflows, hinting at its transition from the AGB phase to the asymmetric planetary nebula phase. In addition, V Hydrae also exhibits a long secondary period of 17 yr in its light curve, suggesting the presence of a binary companion that could shape the circumstellar environment. Aims. In this paper, we aim to confirm the binary nature of V Hydrae by deriving its orbital parameters and investigating the effect of the orbital motion on the circumbinary environment. Methods. In a first step, we used a radial-velocity monitoring performed with the HERMES spectrograph to disentangle the pulsation signal of the AGB from its orbital motion and to obtain the spectroscopic orbit. We combined the spectroscopic results with astrometric information to get the complete set of orbital parameters, including the system inclination. Next, we reported the time variations of the sodium and potassium resonance doublets. Finally, following the methods used for post-AGB stars, we carried out spatio-kinematic modelling of a conical jet to reproduce the observed spectral-line modulation. Results. We found the orbital solution of V Hydrae for a period of 17 yr. We correlated the companion passage across the line of sight with the obscuration event and the blue-shifted absorption of alkaline resonant lines. Those variations were modelled by a conical jet emitted from the companion, whose opening angle is wide and whose sky-projected orientation is found to be consistent with the axis of the large-scale bipolar outflow previously detected in the radio-emission lines of CO. Conclusions. We show that the periodic variation seen for V Hydrae is likely to be due to orbital motion. The presence of a conical jet offers a coherent model to explain the various features of V Hydrae environment.

Impact of Solvents and Extraction Methods on the Insecticidal Activity of <i>Sesbania grandiflora</i> L. Leaf Extracts against Diamondback Moth, <i>Plutella xylostella</i>

Diamond back moth Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a notorious pest of cruciferous crops causing extensive damage. The present study compares the insecticidal activity of Sesbania grandiflora extracts in hexane, ethyl acetate, and ethanol obtained from two extraction methods: Soxhlet and cold maceration against P. xylostella. Soxhlet extraction by all the solvents showed a distinct effect on larval mortality, adult emergence, and the growth and development of second-instar larvae than cold maceration extraction. Soxhlet ethanolic extract at 5% had significantly better insecticidal activity than cold maceration, with complete larval mortality. The antifeedant index was also higher in ethanol extract, followed by ethyl acetate and hexane extract. However, there was no significant variation in the developmental period. Thus, Soxhlet ethanolic extract of S. grandiflora is concluded to have a promising insecticidal activity on P. xylostella.