Large Amplitude Variations Research Articles

Comprehensive analysis of interpolation methods for modeling the spatial distribution of gravity anomalies

Modeling the spatial distribution of gravity anomalies requires accounting for numerous factors that influence the accuracy of results. The primary factors include the interpolation methods used to construct regular grids of gravity anomalies, as well as the distribution and number of observation points. This study compares the accuracy of various interpolation methods for gravity anomalies based on the WGM2012 model. The analysis utilized gravity anomaly data obtained from 200 GNSS stations located in Ukraine and 355 test points of a hypothetical gravimetric network. The research aimed to evaluate the accuracy of interpolation methods such as Inverse Distance to a Power, Kriging, Minimum Curvature, Moving Average, Nearest Neighbor, Polynomial Regression, and Radial Basis Function in tasks of modeling the spatial distribution of anomalies using data from the WGM2012 model. The analysis was performed based on calculated differences between interpolated and original values, supported by graphical and statistical data. The results allowed for the classification of interpolation methods by accuracy: 1) High accuracy with uniform value distribution; 2) Moderate accuracy with a balanced distribution; 3) Low accuracy with large amplitude variations. The study demonstrated that a well-founded selection of an interpolation method can significantly enhance the accuracy of modeling the spatial distribution of gravity anomalies and provide reliable results for solving geophysical problems.

Analysis of axial force variations and seismic performance of subway station columns under earthquake loading

Central column failure is a predominant seismic damage mode in subway station structures. During seismic events, the central columns’ vertical compressive force, as indicated by the axial compression ratio (ACR), undergoes continuous variations, significantly impacting both their failure modes and the seismic performance. This study involved establishing a finite element model of a subway station and conducting time history analyses to identify the distinct variation patterns of ACR in central columns for various seismic design scenarios. Based on these summarized patterns, appropriate ACR variations were designed for the columns, and the validity of the column model was confirmed using experimental data, enabling analyses of their failure modes and hysteresis characteristics under cyclic loads. Lastly, a sensitivity analysis of the parameters associated with the central columns was performed. The results demonstrated that the horizontal displacement and the ACR of the top of the central column were asynchronous, the frequency of the latter was 1.4–3.8 times that of the former, and the amplitude of the ACR was 0.08–0.68. When the frequency of the variable ACR was odd times, the damage and hysteresis curve of the column showed obvious asymmetry and harmfulness, and it exacerbated the damage to the core concrete of the column. Compared to applying a constant ACR, the bearing capacity and energy dissipation of the column were even reduced by about 50 % and 74 %, respectively. The specimens with the upper limit value of 0.95 of variable ACR had even more adverse effects on the damage and hysteresis behavior of the column than the scheme with a constant ACR of 0.95. In addition, the even multiple frequency of variable ACR had a limited effect on the seismic performance of the column, but the harm caused by the large amplitude variation of variable ACR could not be ignored. As to the impacts of structural parameters under cyclic loadings, elevating the longitudinal reinforcement ratio and decreasing the stirrup spacing within the central columns would substantially enhance energy dissipation capacity, with a maximum increase of about 69 %. Meanwhile, for columns with the same cross-sectional area, square columns exhibited superior hysteresis behavior compared to their circular counterparts. The findings of this study could provide guidance for the engineering design of the central columns.

Mapping the dynamics of aquatic vegetation in Lake Kyoga and its linkages to satellite lakes

Lake Kyoga is a shallow, young, flooded basin just north of and about 30m lower than Lake Victoria. The catchment encompasses Lake Kyoga itself, and a constellation of several dozen small satellite lakes following valley contours mostly to its east. The Kyoga basin fish fauna shares many non-cichlid species plus a spectacular, partially endemic radiation of haplochromine cichlids most similar to but still largely distinct from those in Lake Victoria. This fish fauna is of high conservation concern, as it preserves remnants of the regional species flock that have disappeared from Lake Victoria and Lake Kyoga, leaving small remnant populations in some of the satellite lakes. Now, these too are imperiled by limnological dynamics, including fluctuations in the nature and extent of aquatic vegetation. The water bodies in the Kyoga Basin are highly dynamic due both to fluctuation in water level and large amplitude variation in marginal and floating vegetation. This variation has profound evolutionary and conservation implications, since it can create and destroy critical aquatic habitat. It can also alternately anneal and cleave gene flow over time, both between the main lake and its satellites, and among the satellite lakes. The aquatic vegetation cluttering these linkages can create a spatial refugium for many native fish species that are more tolerant of hypoxia than an introduced macropredator, the Nile perch. Anthropogenic impacts to this region have greatly increased in recent years, altering relationships between aquatic vegetation and endangered species, fisheries and other ecosystem services provided by the lake. Understanding these dynamics require a means of mapping aquatic vegetation, connectivity, and habitat through time. Here we develop a new and improved algorithm to map the spatial distribution and dynamics of floating and emergent aquatic vegetation via remote sensing. We utilize a time series of 440 Landsat images dating from 1986 to 2020. A series of water and vegetation indices are designed to reveal change in the aquascape over time. First, two types of water masks are derived using a majority rule - a separate water mask for each image and a composite water mask of the region over the study period. Second, the difference between the two masks is then used to delineate the potential location of macrophytes over the image. Third, an algorithm is developed to separate the floating vegetation from emergent vegetation; this algorithm uses Landsat spectral bands and two additional spatial and temporal metrics that considerably improve classification accuracy. A more extensive analysis of aquascape trajectories using remote sensing can inform fish conservation strategies and fisheries management and illuminate the role of landscape dynamics in macroevolutionary patterns of aquatic taxa.

Nonlinear Characteristics of Radio Variability in Quasar 3C 446

Quasars are characterized by violent and large amplitude variability in all the observation wavelengths, and the analysis of optical variability is useful for developing theoretical models. Long-term optical variability data of quasar 3C 446 were collected from the University of Michigan Radio Astronomy Observatory database in the 4.8, 8.0, and 14.5 GHz radio bands from 1976 to 2012. Due to the complexity of the variability data, it's hard to study by the linear time series analysis methods. For learning more about non-linear characteristics of the temporal evolution of quasar variability, the Ensemble Empirical Mode Decomposition and nonlinear analysis are used to analyse chaotic dynamics, fractal properties, and periodicity. This paper focuses on whether there is a significant difference between the periodic and non-linear properties of the quasar variability before and after the removal of the periodic or chaotic components. It turns out that the variability of quasar 3C 446 in the radio bands consists of periodic, trend, and chaotic components, and the periodic and trend components are dominant. The periods of the variability after removing the chaotic and trend components are exactly the same as the periods of the original variability data, but the chaotic and fractal characteristics of the two are significantly different. The saturated correlation dimension indicates that the reconstruction of the dynamical system requires more independent parameters than the original optical variables after the removal of the periodic and trend components. The Kolmogorov entropy indicates that the loss of information is greater for the former than the latter, and the system is more chaotic and more complex. The Hurst value indicates that the self-similarity and long-range correlation are slightly stronger for the latter than the former.

The Emerging Stellar Complex in Mon R2: Membership and Optical Variability Classification

Monoceros R2 (Mon R2) is one of the closest large active star-forming regions. This extremely young and partially embedded region provides an excellent laboratory for studying star formation and the early evolution of young stellar objects (YSOs). In this paper, we conduct an optical study of the greater Mon R2 region. Beginning with 1690 previously identified candidate YSOs, we used 496 sources with good proper motions and parallaxes from Gaia Data Release (DR) 3 to determine the astrometric properties for likely members of Mon R2. We then used both astrometric and photometric (isochronal and variability) criteria to determine that 308 of these stars are highly probable members. Using the same criteria, we considered a broad area search around Mon R2 in Gaia DR3 and separated candidate members from field stars. In total, we selected 651 likely new cluster members that had been missed in the previous X-ray and infrared excess selection techniques used in the past to establish cluster membership. Revised astrometric properties of the cluster were found using the combined sample of ∼959 highly probable member stars. For the literature plus the new candidate member list, optical light curves were compiled from the Zwicky Transient Facility. For 470 identified variable sources, we attempted classification based on the flux asymmetry (M) and quasiperiodicity (Q) metrics. We find that Mon R2 is dominated by quasiperiodic symmetric variables, with aperiodic sources also a significant population. A few tens of large-amplitude variables are identified that may be of interest for further study.

Multi-periodicity in the high gravity blue large amplitude pulsator ZTF J071329.02-152125.2

Abstract New time series photometry of the pulsating hot subdwarf star ZTF J071329.02-152125.2 is presented. Rapid (timescale of hours) changes in the amplitude of the known pulsation in the star was observed. This could be ascribed to beating between three closely spaced frequencies, but analysis of all available photometry finds a range of different frequencies, with widely different amplitudes. A new frequency of 49.66 d $^{-1}$ , suggestive of gravity-mode pulsation, was also discovered. The star may be a hybrid p-mode/g-mode hot subdwarf pulsator which sometimes exhibits extraordinarily large amplitude variability.

Inviscid modeling of unsteady morphing airfoils using a discrete-vortex method

Abstract A low-order physics-based model to simulate the unsteady flow response to airfoils undergoing large-amplitude variations of the camber is presented in this paper. Potential-flow theory adapted for unsteady airfoils and numerical methods using discrete-vortex elements are combined to obtain rapid predictions of flow behavior and force evolution. To elude the inherent restriction of thin-airfoil theory to small flow disturbances, a time-varying chord line is proposed in this work over which to satisfy the appropriate boundary condition, enabling large deformations of the camber line to be modeled. Computational fluid dynamics simulations are performed to assess the accuracy of the low-order model for a wide range of dynamic trailing-edge flap deflections. By allowing the chord line to rotate with trailing-edge deflections, aerodynamic loads predictions are greatly enhanced as compared to the classical approach where the chord line is fixed. This is especially evident for large-amplitude deformations. Graphical abstract

An Investigation of New Brown Dwarf Spectral Binary Candidates From the Backyard Worlds: Planet 9 Citizen Science Initiative

We present three new brown dwarf spectral-binary candidates: CWISE J072708.09−360729.2, CWISE J103604.84−514424.4, and CWISE J134446.62−732053.9, discovered by citizen scientists through the Backyard Worlds: Planet 9 project. Follow-up near-infrared spectroscopy shows that each of these objects is poorly fit by a single near-infrared standard. We constructed binary templates and found significantly better fits, with component types of L7+T4 for CWISE J072708.09−360729.2, L7+T4 for CWISE J103604.84−514424.4, and L7+T7 for CWISE J134446.62−732053.9. However, further investigation of available spectroscopic indices for evidence of binarity and large amplitude variability suggests that CWISE J072708.09−360729.2 may instead be a strong variability candidate. Our analysis offers tentative evidence and characterization of these peculiar brown dwarf sources, emphasizing their value as promising targets for future high-resolution imaging or photometric variability studies.

Performance-scaled rotor design method for model testing of floating vertical axis wind turbines in wave basins

The wave basin model tests of floating wind turbines typically follow the Froude scaling law, where a geometric-scaled rotor cannot achieve the target thrust due to the Reynolds-number scaling effect. To tackle this issue, a performance-scaled rotor (PSR) has been successfully used in the wave basin model testing of floating horizontal axis wind turbines (HAWTs). Unlike HAWT, the thrust and side forces of a vertical axis wind turbine (VAWT) present periodic and large amplitude variations with the azimuth angle. In this study, a novel PSR design method is proposed for the model testing of floating VAWTs. An alternative airfoil with good aerodynamic performances at low-Reynolds-number is selected to replace the original one. The relationship between the thrust coefficient and the chord length is derived analytically, with accuracy-enhancing corrections. The chord length of the PSR is then determined. The method and procedure are demonstrated by designing and testing a PSR of a 5 MW floating VAWT with three straight blades and a scale ratio of 1:50. Thrust and lateral forces of the floating VAWT are compared and analyzed. Results indicate that the designed PSR can reproduce the thrust and side forces and is applicable for model testing of floating VAWTs.

Mechanism on the Short-Term Variability of the Atlantic Meridional Overturning Circulation in the Subtropical and Tropical Regions

Abstract The continuous, moored observation revealed significant variability in the strength of the Atlantic meridional overturning circulation (AMOC). The cause of such AMOC variability is an extensively studied subject. This study focuses on the short-term variability, which ranges up to seasonal and interannual time scales. A mechanism is proposed from the perspective of ocean water redistribution by layers. By offering explanations for four phenomena of AMOC variability in the subtropical and tropical oceans (seasonality, meridional coherence, layered-transport compensation as observed at 26.5°N, and the 2009/10 downturn that occurred at 26.5°N), this mechanism suggests that the short-term AMOC variabilities in the entire subtropical and tropical regions are governed by a basinwide adiabatic water redistribution process, or the so-called sloshing dynamics, rather than diapycnal processes. Significance Statement The Atlantic meridional overturning circulation (AMOC) is a key component in the global climate system due to its immense power in redistributing heat meridionally, which contributes to the hospitable climate of the United Kingdom and western Europe. Therefore, any changes in AMOC can have significant impacts on both global and local climate variability. Here I propose a mechanism to explain the short-term (up to interannual) AMOC variability in the subtropical and tropical regions from the perspective of ocean water redistribution. This mechanism suggests that the short-term variability of AMOC strength is dominated by an adiabatic process, and thus, its large-amplitude variation is mostly a reversible process. In other words, AMOC may be more resilient to short-term variability than previously believed, and it could recover autonomously from the abrupt changes.

Continuum Reverberation Mapping of Mrk 876 over Three Years with Remote Robotic Observatories

Continuum reverberation mapping probes the size scale of the optical continuum-emitting region in active galactic nuclei (AGN). Through 3 yr of multiwavelength photometric monitoring in the optical with robotic observatories, we perform continuum reverberation mapping on Mrk 876. All wave bands show large-amplitude variability and are well correlated. Slow variations in the light curves broaden the cross-correlation function (CCF) significantly, requiring detrending in order to robustly recover interband lags. We measure consistent interband lags using three techniques (CCF, JAVELIN, and PyROA), with a lag of around 13 days from u to z. These lags are longer than the expected radius of 12 days for the self-gravitating radius of the disk. The lags increase with wavelength roughly following λ 4/3, as would be expected from thin disk theory, but the lag normalization is approximately a factor of 3 longer than expected, as has also been observed in other AGN. The lag in the i band shows an excess that we attribute to variable Hα broad-line emission. A flux–flux analysis shows a variable spectrum that follows f ν ∝ λ −1/3, as expected for a disk, and an excess in the i band that also points to strong variable Hα emission in that band.

Energy and Infrared Radiation Characteristics of the Sandstone Damage Evolution Process.

The mechanical characteristics and mechanisms of rock failure involve complex rock mass mechanics problems involving parameters such as energy concentration, storage, dissipation, and release. Therefore, it is important to select appropriate monitoring technologies to carry out relevant research. Fortunately, infrared thermal imaging monitoring technology has obvious advantages in the experimental study of rock failure processes and energy dissipation and release characteristics under load damage. Therefore, it is necessary to establish the theoretical relationship between the strain energy and infrared radiation information of sandstone and to reveal its fracture energy dissipation and disaster mechanism. In this study, an MTS electro-hydraulic servo press was used to carry out uniaxial loading experiments on sandstone. The characteristics of dissipated energy, elastic energy, and infrared radiation during the damage process of sandstone were studied using infrared thermal imaging technology. The results show that (1) the transition of sandstone loading from one stable state to another occurs in the form of an abrupt change. This sudden change is characterized by the simultaneous occurrence of elastic energy release, dissipative energy surging, and infrared radiation count (IRC) surging, and it has the characteristics of a short duration and large amplitude variation. (2) With the increase in the elastic energy variation, the surge in the IRC of sandstone samples presents three different development stages, namely fluctuation (stage Ⅰ), steady rise (stage Ⅱ), and rapid rise (stage Ⅲ). (3) The more obvious the surge in the IRC, the greater the degree of local damage of the sandstone and the greater the range of the corresponding elastic energy change (or dissipation energy change). (4) A method of sandstone microcrack location and propagation pattern recognition based on infrared thermal imaging technology is proposed. This method can dynamically generate the distribution nephograph of tension-shear microcracks of the bearing rock and accurately evaluate the real-time process of rock damage evolution. Finally, this study can provide a theoretical basis for rock stability, safety monitoring, and early warning.

The Behavior of Bp He-weak Stars in the Far UV—Paper VI: HD 21699

The analysis of spectra of the B8 He-weak Si star HD 21699 recorded by the SWP camera on board the International Ultraviolet Explorer in 1987 reveals large amplitude variations of the far-ultraviolet spectral energy distribution over a time interval of about four days in 1987 October. In contrast, the level of the mid-UV flux did not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The lines of C iv doublet near 1550 Å are stronger and have an extended blue wing at phase of far-UV maximum. The optical brightness recorded by the Fine Error Sensor on board IUE is probably anticorrelated with the FUV flux, reflecting the redistribution of the FUV flux toward longer wavelengths.

The Behavior of Bp Si Stars in the far-UV—Paper VI: HD 215441

The analysis of spectra of the B9 Si star HD 215441 recorded by the SWP camera on board the International Ultraviolet Explorer reveals large amplitude variations of the far-ultraviolet spectral energy distribution over a time interval of about half the rotation period. In contrast, the level of the mid-UV flux does not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The optical brightness recorded by the Fine Error Sensor on board IUE is anticorrelated with the FUV flux, reflecting the redistribution of the FUV flux towards longer wavelengths.

Weather image-based short-term dense wind speed forecast with a ConvLSTM-LSTM deep learning model

Short-term wind speed predication is of great significance for scholars (e.g., understanding wind profiles), practitioners (e.g., building energy management), regulators (e.g., urban microclimate regulation), and even the general public. Current wind speed forecasting methods either generate sparse predictions or occur high cost. This paper reports a novel, inexpensive framework to forecast urban local dense wind speed. The central tenet is a convolutional long short-term memory (ConvLSTM) and LSTM combinatorial deep learning model to learn the features of input historical weather image series coupled with spatial-temporal correlations. The model was trained and tested using Hong Kong datasets. The feasibility and effectiveness of the proposed model are verified and compared with parallel models under different criteria, including mean absolute error (MAE), root mean square error (RMSE) and R-squared (R2). The experimental results show that: (1) the proposed ConvLSTM-LSTM deep learning model can effectively forecast wind speed regardless of location; (2) the overall MAE, RMSE, and R2 value of the proposed model are improved by 14.84%, 15.04%, and 7.51%, respectively, compared to the ConvLSTM-full connected (ConvLSTM-FC) model, and by 22.12%, 22.80%, and 12.24%, respectively, compared to the convolutional neural network-LSTM (CNN-LSTM) model; and (3) compared with parallel models, the proposed model has better performance in predicting wind speed series with large amplitude variations and rapid frequency changes.

The Behavior of Bp Si Stars in the Far UV—Paper V: HD 187473

The analysis of five spectra of the B9 SiSrEu HD 187473 recorded by the Short Wavelength Prime camera on board the International Ultraviolet Explorer reveals large amplitude variations of the far ultraviolet spectral energy distribution over a time interval of about half the rotation period. In contrast, the level of the mid-UV flux does not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The iron-peak elements, chromium, manganese and iron probably also contribute to these variations.

Crosshole Ground‐Penetrating Radar in Clay‐Rich Quaternary Deposits: Toward Characterization of High‐Loss Media

AbstractKnowing the centimeter‐to meter‐scale distribution of sand in clayey deposits is important for determining the dominating water flow pathways. Borehole information has a high vertical resolution, on the millimeter‐ to centimeter‐scale, but provides poor lateral coverage. For highly heterogeneous deposits, such as glacial diamicts, this detailed borehole information may not be sufficient for creating reliable geological models. Crosshole ground‐penetrating radar (GPR) can provide information on the decimeter‐ to meter‐scale variation between boreholes, but has mainly been used in sandy environments. In this study, we investigate whether crosshole GPR can provide information on the structural relationship of diamicts and their material properties, such as water content, bulk density, and clay content. To achieve ground truth, we compare the crosshole GPR data with geological information from boreholes and an excavation at the field site. The GPR data was analyzed comprehensively using several radar wave attributes in both time‐ and frequency domain, describing the signal velocity, strength, and shape. We found small variations in signal velocity (between 0.06 and 0.07 m/ns) but large variations in both amplitude and shape (either order of magnitude variation or doubling/tripling of attribute values). We see that the GPR response from wetter and more clayey diamicts have both lower amplitudes and lower centroid frequencies than the response from their drier and sandier counterparts. Lastly, we find that the variation in amplitude and shape attributes is better correlated to the diamicts' material properties than the signal velocity.

Long-term Photometric Study of the Pre-main Sequence Star V1180 Cas

In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported. The star is a young variable associated with the dark cloud Lynds 1340, located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia. V1180 Cas shows large amplitude variability, interpreted as a combination of accretion-induced and extinction-driven effects. Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022. During our monitoring, we recorded several brightness dips with large amplitudes of up to 5 mag (I band). At the same time, increases in brightness over periods of several weeks have also been recorded. In this paper, we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.

Multiple forcing on Late Miocene East Asian Summer Monsoon Precipitation Variability in NE Tibetan Plateau

Understanding how the East Asian Summer Monsoon (EASM) evolves at different time scales affords a valuable opportunity to reveal the interactions between the hydrosphere, land, oceans and atmosphere. However, the pre-Quaternary evolutionary history and the driving forces that controlled its variability in response to different boundary conditions remain enigmatic. Here, we focus on the late Miocene (∼10.8 to 6.3 Ma) – a period of profound climatic and topographic changes in Asia – and present a quantitative reconstruction of EASM precipitation using the probabilistic CREST (Climate Reconstruction Software) method with a high temporal resolution pollen record from the Tianshui Basin in NE Tibetan Plateau (TP). Our new EASM precipitation record shows a slowly decreasing long-term trend during the period of ∼ 10.8–7.6 Ma, which was followed by a strengthening period from ∼ 7.6 to 6.3 Ma with a large amplitude of precipitation variability. We argue the decrease and increase periods of EASM precipitation were primarily response to late Miocene global cooling and TP uplift after ∼ 8 Ma, respectively. These results are supported by existing climate model simulations, wherein both global climate and paleotopography play key roles in regulating the long-term evolution of late Miocene EASM. On orbital time scales, the precipitation time series exhibit a dominant ∼ 410 kyr eccentricity periodicity, with lower (higher) values intervals corresponding to eccentricity minima (maximum). The synchronous phase of the precipitation and eccentricity records indicate that the eccentricity exerts a dominant influence on the EASM precipitation cycles via its modulation of the precessional amplitude, and the period expansion and contraction of Antarctic ice sheet (AIS) also probably play an important role during that time. Our quantitative late Miocene EASM precipitation records provide new insight into late Miocene EASM precipitation evolution and its relation with global climate, paleotopography, and cryosphere.

The local energy flux surrogate in turbulent open-channel flows

We present a local analysis of turbulence in open-channel flows, using time-series velocity measurements. The method is based on a local form of the Kolmogorov “4/3-law” of homogeneous turbulence for the third-order moment of velocity increments. Following the Duchon and Robert [“Inertial energy dissipation for weak solutions of incompressible Euler and Navier–Stokes equations,” Nonlinearity 13, 249 (2000)] idea, which envisions turbulence dissipation as a lack of smoothness of the Navier–Stokes solutions, we estimate the local energy flux in a laboratory experiment with natural bed flows. Taking advantage of one-dimensional filtering techniques, under reasonable hypothesis, simple expressions of a surrogate of the energy flux are provided. The local energy flux surrogate reveals that, independently of the geometry, turbulence dissipation is highly intermittent. Among a variety of eddies that populate turbulence, dissipative singularities appear in sheet-like, tube, and filament structures, with large amplitude variations and rotations. This simplified technique can be applied to any measurement of hydrodynamic turbulence.