Unimodal Spectra Research Articles

Frequency Spectrum Is More Effective for Multimodal Representation and Fusion: A Multimodal Spectrum Rumor Detector

Multimodal content, such as mixing text with images, presents significant challenges to rumor detection in social media. Existing multimodal rumor detection has focused on mixing tokens among spatial and sequential locations for unimodal representation or fusing clues of rumor veracity across modalities. However, they suffer from less discriminative unimodal representation and are vulnerable to intricate location dependencies in the time-consuming fusion of spatial and sequential tokens. This work makes the first attempt at multimodal rumor detection in the frequency domain, which efficiently transforms spatial features into the frequency spectrum and obtains highly discriminative spectrum features for multimodal representation and fusion. A novel Frequency Spectrum Representation and fUsion network (FSRU) with dual contrastive learning reveals the frequency spectrum is more effective for multimodal representation and fusion, extracting the informative components for rumor detection. FSRU involves three novel mechanisms: utilizing the Fourier transform to convert features in the spatial domain to the frequency domain, the unimodal spectrum compression, and the cross-modal spectrum co-selection module in the frequency domain. Substantial experiments show that FSRU achieves satisfactory multimodal rumor detection performance.

Analysis of Unidirectional Wave Spectral Characteristics in the Northeastern Waters of Taiwan

Marine energy development has been actively promoted in recent years. Analyzing wave data in the surrounding sea areas is crucial for improving wave power generator efficiency. This study collected unidirectional wave spectrum data from the northeast coastal area of Taiwan (e.g., Pengjia Islet, Fugui Cape, and NTOU). It aimed to analyze the main wave types (i.e., wind waves, swell, or mixed sea) and their proportions during the northeast and non-northeast monsoon periods. The results indicate that swell waves dominate at the NTOU buoy, while wind waves dominate at the other two stations. In addition, the analysis of wave spectra ratios revealed a low percentage of unimodal spectra (only about 0.5%), and bimodal and unformed spectra presented as predominant. Furthermore, this study also introduced a brand new JW-J wave spectrum, which combines the JW and JONSWAP spectra to describe low-frequency (swell) and high-frequency (wind wave) systems, showing superior performance compared to the Torsethaugen spectrum. Finally, this research analyzed the JW-J spectrum parameters from the Pengjia Islet and Fugui Cape stations and applied these results to the NTOU bouy for effectively describing wind/swell wave variations.

Resources and ontogenetic structure of cenopopulations of the genus Viola (Violaceae, Magnoliópsida) in the Right Volga bank of the Saratov region

The results of our studies of resources and the state of coenopopulations of three species from the genus Viola, namely, V. canina L., V. tricolor L., and V. arvensis Murray, conducted in Romanovsky, Balashovsky and Kalininsky districts of the Saratov region in 2016–2021 are presented. Descriptions of the species’ habitats with geographic coordinates are given. The species V. canina, V. tricolor, and V. arvensis have medicinal, honey-providing and decorative value. Populations of the species are confined to meadow-steppe grass-forb phytocenoses. The phytocenoses with the participation of the studied species differ in dominant and codominant species. As a result of our study of the ontogenetic structure of V. canina cenopopulations (CP), it was found that both CPs have unimodal spectra with a maximum on plants of the virginal group. The cenopopulation type according to the «delta-omega» criterion is transitional. The CP of V. tricolor and CP 2 of V. arvensis are characterized by average reproduction efficiency. The CP 1 of V. arvensis has low reproduction efficiency; the value of the recovery index of its age spectrum is less than one. Regeneration processes in CP 1 of V. arvensis are difficult and unstable. Our analysis of the age structure of CPs using the delta-omega classification has shown that the CP of V. tricolor and CP 1 of V. arvensis are maturing, while CP 2 of V. arvensis is transitional by its position in the delta-omega coordinate system. The yield of the species depended on the degree of moisture in the year. On average, over 5 years of the study, the yield of V. arvensis, V. canina and V. tricolor was 21.51, 19.09 and 27.2 t/ha, respectively. In order to restore the populations, the exploitation of thickets of all species of the genus Viola should be carried out once every three years on 1/3 of the area of thickets.

Эколого-биологические особенности пижмы обыкновенной (Tanacetum vulgare L.) в экотопах Кабардино-Балкарской Республики

The bulk of the preparations of medicinal plant raw materials of common tansy (Tanacetum vulgare L.) are wild plants. Flores Tanaceti industrial collections are produced in the central regions of the European part of Russia. In the North Caucasus, T. vulgare grows scattered, so the data on the bioresource potential of the species require clarification. The aim of the study was to study the ecological and biological features of T. vulgare in the ecotopes of the Kabardino-Balkarian Republic (KBR). The study of the area, morphological and phytochemical variability of T. vulgare was carried out on the territory of the KBR in 2018-2021 at the start of flowering plants.The study of the range, ontogenesis and ecological and biological features of T. vulgare was carried out on the territory of the KBR in 2018-2021 at the start of flowering plants. According to the results of the study, the range of T. vulgare covers three floristic subregions: Chegemo-Chereko-Sukansky, Leskeno-Lashkutinsky and Jurassic depressions. The highest occurrence and abundance of plants are typical for forest, forest-steppe, meadow, floodplainecotopes of the foothill zone of the KBR. In the studied phytocenoses, T. vulgare is a companion species with an average abundance of 0,3-2,5%. The zone of ecological optimum for the species is meadow-steppe and drymeadow moisture, fairly rich soils, moderate moisture variability, and weak pasture digression. Under conditions of low load, T. vulgare cenopopulations form normal full-membered, unimodal spectra with a maximum on mature generative specimens. Under stress conditions, the spectra become incomplete, discontinuous, unimodal, right-handed, with a maximum on old-aged generative plants. Among the studied morphological and economically valuable traits of T. vulgare, high variability was noted for the number of anthologies in the inflorescence, medium variability for the number of generative shoots and flower yield, low and very low variability for the height of the shoot, the content of phenolic substances, and the diameter of the anthorax. In mid-mountain cenopopulations compared with foothill a significant increase in the content of the sum of flavonoids and phenolcarboxylic acids in flowers, shoot height, a decrease in the number of baskets in the inflorescence, the number of generative shoots, and the yield of raw materials were found. The nature of the correlation between the accumulation of phenolic compounds in flowers and the studied morphological traits can be used to select T. vulgare ecotypes and include them in the breeding process.

Magnetism and Grain-Size Distribution of Particles Deposited on the Surface of Urban Trees in Lanzhou City, Northwestern China.

Studies on the variation in the particulate matter (PM) content, Saturation Isothermal Remanent Magnetization (SIRM), and particle grain-size distribution at a high spatial resolution are helpful in evaluating the important role of urban forests in PM removal. In this study, the trees located in dense urban forests (T0) retained more PM than trees located in open spaces (T1–T4); the SIRM and PM weight of T0 were 1.54–2.53 and 1.04–1.47 times more than those of T1–T4, respectively. In addition, the SIRM and PM weight decreased with increasing distance to the road, suggesting that distance from pollution sources plays a key role in reducing the air concentration of PM. The different grain-size components were determined from frequency curve plots using a laser particle-size analyzer. A unimodal spectrum with a major peak of approximately 20 μm and a minor peak between 0.1 and 1 μm was observed, indicating that a large proportion of fine air PM was retained by the needles of the study trees. Additionally, more <2.5 μm size fraction particles were observed at the sampling site near the traffic source but, compared to a tree in a row of trees, the percentage of the >10 μm size fraction for the tree in the dense urban forest was higher, indicating that the particles deposited on the needle surface originating from traffic sources were finer than those from natural atmospheric dust. The exploration of the variation in the PM weight, SIRM, and grain size of the particles deposited on the needle surface facilitates monitoring the removal of PM by urban forests under different environmental conditions (e.g., in closed dense urban forests and in open roadside spaces), different distances to roads, and different sampling heights above the ground.

Observations of surface wave fields in the Arabian Sea under tropical cyclone Tauktae

The characteristics of surface wave fields in the eastern Arabian Sea under tropical cyclone Tauktae were investigated using buoy data. On May 16, 2021, the cyclone passed within 96 km of the buoy location, and a maximum wave height of 9.7 m with a significant wave height of 5.6 m was recorded by the buoy, moored at 23.5 m water depth off Goa. As the cyclone approached the buoy location, a shift in the frequency caused waves to turn into unimodal spectra with high wave energy and spectral peak parameter. Further, the evolution of cyclone-induced waves and their spatial variation have been investigated using the ERA5 reanalysis data. The results suggest that for distances of ∼400 km spatial extend from the cyclone's eyewall, the cyclone induced waves to have a high impact with significant wave height above 3 m for a cyclone sustained wind speed of around 100–120 knots. The dominance of wind-seas over swells and the directional shift are noticeable, specifically along the west coast of India during the tropical cyclone passage.

Dual-energy x-ray approach for object/energy-specific attenuation coefficient correction in single-photon emission computed tomography: effects of contrast agent.

Purpose: To investigate the influence of radiographic contrast agent on the accuracy of the photon counts arising from the emission of gamma rays of radionuclides in single-photon emission computed tomography (SPECT), when dual-energy x-ray CT (DXCT) is employed for providing object/energy-specific attenuation coefficient correction in SPECT. Approach: Computer simulation was performed for three transmission CT approaches, namely, the conventional (single kVp, unimodal spectrum) x-ray CT, DXCT (single kVp, bimodal spectrum) with basis material decomposition (BMD), and DXCT with BMD followed by basis material coefficients transformation (BMT), to study the effects of these approaches on the accuracy of the photon counts from the SPECT image of a thorax-like phantom. Results: All three CT approaches revealed that the error in the counts was both photon energy and iodine concentration-dependent. Differences in the trending increase/decrease in the errors with the respective increase in iodine concentration and photon energy were observed among the three CT approaches. Of the three, the BMT/SPECT approach resulted in the smallest error in the concentration of radionuclides measured, especially in the contrast agent-filled region, and the optimal level depended on the iodine concentration and photon energy. Conclusion: With a judicious choice of the basis materials and photon energy, it may be possible to take advantage of the benefits of the BMT method to mitigate the accuracy problem in DXCT for quantitative SPECT imaging.

SPECTRAL ANALYSIS OF STORM-INDUCED WAVES BY CYCLONE ASHOBAA IN ARABIAN SEA AND GULF OF OMAN

Extensive field measurements along the north coast of the Gulf of Oman are analyzed to study the spectral characteristics of the generated waves of Ashobaa along the path of cyclone. The data showed a maximum significant wave height of about 3.2 meters on Iranian coasts. MLMST algorithm was used to process the directional wave. The measured wave spectra were bimodal (or trimodal) when the cyclone was far from the measuring stations. Approaching closer to the stations, the waves turned to unimodal spectra, with the highest measured wave energies at the time of minimum distance between the cyclone eye and the stations. Wave spectrum became bimodal again at the time of landfall, including the local seas and swell waves of the cyclone. After dissipation of the cyclone, swell waves dominate resulting in unimodal wave spectra. Study of 2D wave spectra reveals that minimum values of directional spreading correspond to peak frequencies.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/k9Bs4TebgdE

Numerical modeling of hydrogen thermal desorption peaks

Various mathematical models are used for investigation of the thermal desorption spectra (TDS spectra) of hydrogen isotopes, in particular, in the form of a first-order reaction for the volume-averaged concentration (in the case of diffusion limitation), second-order models (taking into account the recombination of hydrogen atoms on the surface into molecules) and more detailed models reflecting multistage transport (volume diffusion, outlet to the surface, recombination, desorption). Interest is the analysis of the structure of the spectrum in order to identify the causes and "driving forces" of a physical and chemical nature corresponding to each peak. The article presents an analysis of the symmetry of unimodal TDS spectra and the results of simulation.

Time-frequency analysis for two cases of boundary-layer transition induced by random distributed roughness

The boundary layer transition induced by distributed surface roughness has great practical relevance, but remains poorly understood. In this experimental work, we investigate the transition in a flat-plate boundary layer downstream of a localized strip of random distributed roughness. The boundary layer exhibits different temporal and spectral behaviour in two (roughness-) Reynolds-number regimes separated by a critical value. In the “sub-critical” regime, the velocity signals show presence of “turbulent spots”, whereas in the “super-critical” regime, no distinct turbulent spots are observed. Two boundary-layer profiles, one each from the sub-critical and super-critical regimes, are chosen for comparison. The sub-critical case exhibits a bi-modal power spectrum having two humps in frequency ranges differing by an order of magnitude, whereas the super-critical case has a uni-modal spectrum with a single hump in the high-frequency range. The wavelet analysis shows that the energy distribution is intermittent in time for both the cases at all frequencies. However, for the sub-critical case, the energy in the high-frequency range appears as clusters, which are seen as turbulent spots in the velocity signal. On the other hand, for the super-critical case there is no such clustering, consistent with the absence of spots in the velocity signal. We conjecture that, for the sub-critical case, the motions corresponding to the low-frequency spectral hump (possibly the streamwise streaks) could be responsible for imparting organization to the high-frequency motions in the form of turbulent spots. We also detect “events” in the wavelet-energy time series. For the sub-critical case, the events in the high-frequency range have a higher degree of time-localization, which increases with frequency. For the super-critical case, however, the time-localization is independent of frequency over nearly the entire frequency range. These findings present two different scenarios for the late stages of transition, having distinct time-frequency behaviour. This could have implications towards modelling roughness-induced transition.

Parametric Spectral Analysis of Noisy Signals with Unimodal Spectrum

The article proposes a method for the coefficients reconstruction of a discrete autocorrelation function of random signals with a unimodal power spectral density to construct their parametric models. The method is based on finding the optimal values of the relative width ΔFT and the weighting factor α in [0; 1] of the spectral mode, which characterizes the share of the Gaussian and resonant components in the spectrum envelope. The proposed method makes it possible to reduce by 1.5–4 times the discrepancy between the control and estimated spectra in comparison with the known approaches to parametric spectral analysis. An increase in the adequacy of spectral estimation makes it possible to reduce the length M of the analyzed time sample by a factor of 2.3–4 times, while maintaining the accuracy of the spectral analysis achieved by other known parametric methods. Winnings are achieved by using a priori information about the spectral properties of the analyzed process.

Impact of the four-wave quasi-resonance on freak wave shapes in the ocean

Two freak waves were observed a day apart in October 2009 at a 5000-m deep moored station in the northwest Pacific Ocean. As the typhoon passed by, the wave system transitioned within a day from a narrow and unimodal spectrum to the broad and bi-modal spectrum. The occurrence probability of a freak wave is known to increase due to a modulational instability; however, whether the modulational instability survives under a realistic directional sea state has not been conclusively determined yet. In this study, a phase-resolving wave model was used to obtain ensembles of realizations based on observed and simulated directional spectra. Unlike previous studies that focused only on the probability of freak wave occurrence, this study focuses on wave shape. It reveals that the front-to-rear asymmetry and crescent shape deformation of the crest are more pronounced for narrower spectrum and longer-lifetime freak waves; this distortion of wave shape and extended lifetime are both characteristics of nonlinear wave groups. This study also shows that the distribution of the lifetime of a freak wave depends on the sea state and that the number of nonlinear wave groups increases for a narrower spectrum. We therefore conjecture that both the four-wave quasi-resonance and dispersive focusing are responsible for freak wave generation, but their relative significance depends on the spectral broadness. Investigating the total kurtosis or occurrence probability alone is insufficient to unravel the underlying mechanisms of individual freak-wave generation.

Temporal information processing in gray treefrogs: Compute within frequency then integrate across frequency

In Cope’s gray treefrog (Hyla chrysoscelis), the pulse rate of advertisement calls is a species recognition cue. This temporal information is redundant across two spectral bands in the call’s bimodal spectrum that are primarily transduced by different inner ear papillae. Previous studies have shown that some neurons in the frog auditory midbrain are selective for bimodal spectra and that, compared with unimodal spectra, calls with bimodal spectra are more attractive. In addition, “interval-counting” neurons in the frog auditory midbrain are selective for conspecific pulse rates. However, it is not known whether pulse rate information is computed prior to, or subsequent to, spectral integration. We conducted behavioral experiments to investigate the serial order of pulse rate computations and spectral integration. In phonotaxis tests that used bimodal and unimodal stimuli with variable pulse rates, we tested the hypothesis that spectral information is integrated prior to pulse rate computations versus the alternative hypothesis that pulse rate can be computed independently in different frequency channels prior to spectral integration. Our results support the latter hypothesis, and suggest pulse rate can be computed independently in separate frequency channels. These results give insight into the mechanisms of temporal processing underlying the perception of key biological information.

Tracking the evolution of Late Mesozoic arc-related magmatic systems in Hong Kong using in-situ U-Pb dating and trace element analyses in zircon

The links between large-scale silicic volcanism and plutonism offer insights into the dynamics of crustal magmatic systems and growth of continental crust. In Hong Kong, voluminous silicic ignimbrites and linked plutons record a ~26 Myr period of magmatism from ~164 to 138 Ma. We present data from these linked volcanic-plutonic assemblages at the Lantau and High Island caldera complexes, with an emphasis on the ~143–138 Ma activity from the latter. To track the evolution of these magmatic systems, U-Pb dating and trace element analyses using secondary-ion mass spectrometry (SIMS) were carried out on zircons from 21 samples from both volcanic and plutonic samples. The SIMS age data sets divide into two groups across volcanic and plutonic origins: (1) seven samples with unimodal age spectra [five of which have the same mean value as the published Isotope Dilution Thermal Ionization Mass Spectrometry (ID-TIMS) age from the same sample]; and (2) 14 samples yielding multiple age components. Age patterns from both groups suggest that the previously separated ~143 Ma Repulse Bay (RBVG) and ~141–140 Ma Kau Sai Chau volcanic groups (KSCVG) instead represent activities over a single ~5 Myr period. Direct linkages previously proposed between some volcanic and plutonic units for this period (e.g., High Island Tuff, Kowloon Granite) are no longer supported, and magmatism represented by exposed plutons continued until 137.8 ± 0.8 Ma (Mount Butler Granite). Under CL imagery, a wide range of zircon textures identified in both volcanic and plutonic samples is indicative of complex processes, some of which are identified through trace element data coupled with textural characteristics. Overall, intra-grain (cores vs. rims; sector-zonation) and intra-sample variations in trace element abundances and ratios are larger than those between samples. Zircon chemistries in both volcanic and plutonic samples fall into two groups during the ~5 Myr history of the High Island caldera magmatic system. One group (RBVG and “cold” granites) includes inherited grains back to 164 Ma and wider ranges in Hf, Y, total trivalent elements, Th and U concentrations and Th/U, Yb/Gd, and U/Yb ratios than the other (KSCVG and “hot” granites). Two possible evolutionary models of the High Island caldera magmatic system are: (1) the system randomly tapped a single crustal domain that fluctuated in temperature as a result of varying interactions of hotter melts, or (2) the volcanic and plutonic records reflect the interplay of two crustal domains with contrasting “low-” and “high-temperature” characteristics. In Hong Kong, some plutonic bodies were comagmatic with large-scale volcanism, while others were emplaced at shallow crustal levels independently of volcanism, matching the current two end-member views of the volcanic-plutonic relationship.

Fluctuation spectra and force generation in nonequilibrium systems

Many biological systems are appropriately viewed as passive inclusions immersed in an active bath: from proteins on active membranes to microscopic swimmers confined by boundaries. The nonequilibrium forces exerted by the active bath on the inclusions or boundaries often regulate function, and such forces may also be exploited in artificial active materials. Nonetheless, the general phenomenology of these active forces remains elusive. We show that the fluctuation spectrum of the active medium, the partitioning of energy as a function of wavenumber, controls the phenomenology of force generation. We find that, for a narrow, unimodal spectrum, the force exerted by a nonequilibrium system on two embedded walls depends on the width and the position of the peak in the fluctuation spectrum, and oscillates between repulsion and attraction as a function of wall separation. We examine two apparently disparate examples: the Maritime Casimir effect and recent simulations of active Brownian particles. A key implication of our work is that important nonequilibrium interactions are encoded within the fluctuation spectrum. In this sense, the noise becomes the signal.

Validation of the Boccotti's generalized model for large nonlinear wave heights from laboratory mixed sea states

The presented work aims at validating the generalization of the asymptotic distribution model of Boccotti for large wave heights recently proposed by Tayfun [1] to laboratory generated mixed sea states with two-peak spectra. The input wave spectra are modelled as the sum of two JONSWAP spectra describing unidirectional wave systems with different or identical directions of propagation (crossing or following mixed seas). In order to account for the effect of the energetically dominant wave system on the largest observed waves, the Boccotti's parameters were calculated at the absolute minimum of the autocorrelation function which can differ from the first minimum for some cases of mixed seas, such as those dominated by the swell or seas with comparable contribution of the two spectral components. So far the proposed model has been validated elsewhere against samples of large wave heights exceeding the significant wave height in wind seas and in mechanically generated long-crested seas, both characterized by unimodal spectra and strong third-order nonlinearities. The present study demonstrates that it can predict equally well the tail of the distributions for mixed seas, irrespective of the type of the mixed sea, particularly when the third-order statistics is relatively large. Typically, the mixed seas from the considered offshore basin experiment display such conditions as the propagation distance from the wavemaker increases, though this effect is less pronounced for mixed following than for mixed crossing wave conditions. Moreover, the generalized model remains valid irrespective of the sign of the fourth-order sum Λ which is a key parameter of the distribution. Its good predictive ability is quantified here by the root-mean-square errors between observations and theory.

Wave energy conversion by controlled floating and submerged cylindrical buoys

This paper investigates the wave energy conversion performance of floating and submerged heaving vertical-cylinder buoys. Two types of reactive control strategies are evaluated for their effect on energy absorption in irregular waves described by uni-modal spectra. Approximate near-optimal reactive control based on up-wave surface elevation measurement and peak-frequency tuning are compared for performance improvements over constant-damping load. The paper describes time-domain calculations under unconstrained oscillation in long-crested irregular waves for two sets of buoy dimensions. Supporting analysis and frequency-domain calculations suggest that near-optimal control performs considerably better than peak-frequency tuning for the submerged buoys and somewhat better for the floating buoys. The relative contributions of the Froude–Krylov and diffraction force components, and wave radiation properties for the two configurations are found to be important in this context.

Comparative Analysis of DNA Word Abundances in Four Yeast Genomes Using a Novel Statistical Background Model

Previous studies have shown that the identification and analysis of both abundant and rare k-mers or “DNA words of length k” in genomic sequences using suitable statistical background models can reveal biologically significant sequence elements. Other studies have investigated the uni/multimodal distribution of k-mer abundances or “k-mer spectra” in different DNA sequences. However, the existing background models are affected to varying extents by compositional bias. Moreover, the distribution of k-mer abundances in the context of related genomes has not been studied previously. Here, we present a novel statistical background model for calculating k-mer enrichment in DNA sequences based on the average of the frequencies of the two (k-1) mers for each k-mer. Comparison of our null model with the commonly used ones, including Markov models of different orders and the single mismatch model, shows that our method is more robust to compositional AT-rich bias and detects many additional, repeat-poor over-abundant k-mers that are biologically meaningful. Analysis of overrepresented genomic k-mers (4≤k≤16) from four yeast species using this model showed that the fraction of overrepresented DNA words falls linearly as k increases; however, a significant number of overabundant k-mers exists at higher values of k. Finally, comparative analysis of k-mer abundance scores across four yeast species revealed a mixture of unimodal and multimodal spectra for the various genomic sub-regions analyzed.

Identification of Swell in Nearshore Surface Wave Energy Spectra

An approach for routine identification of swell and sea in nominally fully developed, omnidirectional, surface water wave energy spectra measured in arbitrary water depth is developed, applied, and discussed. The methodology is an extension of earlier work with deepwater spectra and involves identifying the frequency at which wave steepness is maximized and relating this to the swell separation frequency. The TMA parameterized spectrum is employed to establish a relationship between the two frequencies so that the methodology can be used when wind data are unavailable. The methodology is developed for finite water depth and tested using a dataset that includes both acoustic Doppler current profiler and wave buoy data, recorded simultaneously at the same location. For cases where the sea and swell are clearly, visually distinguishable in the omnidirectional spectra, the new method accurately distinguishes between the two, but it can also be used to identify sea and swell in unimodal spectra.

Analytic continuation average spectrum method for quantum liquids

We revisit the problem of determining the real-frequency density response in quantum fluids via analytical continuation of imaginary-time quantum Monte Carlo data. We demonstrate that the average spectrum method (ASM) is capable of revealing resolved modes in the dynamic structure factor of both ortho-deuterium and liquid para-hydrogen, in agreement with experiments and quantum mode-coupling theories, while the maximum entropy approach yields only a smooth unimodal spectrum. Outstanding issues are discussed. Our work provides the first application of the ASM method in realistic off-lattice systems.