Spectral Character Research Articles

A One-Dimensional Model for Investigating Scale-separated Approaches to the Interaction of Oceanic Internal Waves

Abstract High-frequency wave propagation in near-inertial wave shear has, for four decades, been considered fundamental in setting the spectral character of the oceanic internal wave continuum and for transporting energy to wave-breaking. We compare idealized ray tracing numerical results with metrics derived using a wave turbulence derivation for the kinetic equation and a path integral to study this specific process. Statistical metrics include the changing ensemble mean vertical wavenumber, referred to as a mean drift, dispersion about the mean drift, time lagged correlation estimates of wavenumber and phase locking of the wave packets with the background. The path integral permits us to identify the mean drift as a resonant process and dispersion about that mean drift as non-resonant. At small inertial wave amplitudes; ray tracing, wave turbulence and the path integral provide consistent descriptions for the mean drift of wavepackets in the spectral domain and dispersion about the mean drift. Extrapolating these results to the background internal wavefield over-predicts downscale energy transports by an order of magnitude. At oceanic amplitudes, however, the numerics support diminished transport and dispersion that coincide with the mean drift time scale becoming similar to the lagged correlation time scale. We parse this as the transition to a non-Markovian process. Despite this decrease, numerical estimates of downscale energy transfer are still too large. We argue that residual differences result from an unwarranted discard of Bragg scattering resonances. Our results support replacing the long standing interpretive paradigm of extreme scale-separated interactions with a more nuanced slate of ‘local’ interactions in the kinetic equation.

Dynamics and spectral character of unsteady pressure field on afterbody of generic space launcher: Transonic flows

The unsteady pressure field over an axisymmetric backward-facing step was investigated experimentally at transonic freestream Mach numbers of 1.05, 1.2, and 1.4. The study was aimed at examining the influence of transonic freestream Mach numbers on the spatio-temporal character of the unsteady pressure field and on the dominant modes/mechanisms driving it. Surface flow visualization, schlieren, and unsteady pressure measurements were carried out as part of the experimental investigation. From oil flow visualization and schlieren, the reattachment region was identified, and consequently, the mean reattachment length was estimated. The mean reattachment length shows an increase with the increase in freestream Mach number. The coefficient of mean pressure along the rearbody imitates a classical backward-facing step flow profile and can be divided into three distinct regions. The peak values of the coefficient of mean pressure and the coefficient of root mean square of the fluctuation are seen to decrease with an increase in the freestream Mach number. Conventional spectral analysis reveals that as the freestream Mach number increases, the dominant peak in the spectra shifts to lower frequencies. From the spectra, three dominant fluid dynamic mechanisms depending on the freestream Mach number have been identified. Proper Orthogonal Decomposition (POD) analysis shows that 79–84 % of the total energy contribution comes from the first six modes. The temporal dynamics of the POD modes indicate three prominent mechanisms are responsible for the unsteady pressure field. Spectral analysis of POD modes indicates that the spectra are primarily driven by the first three POD modes for freestream Mach number of 1.05 and the first two modes for freestream Mach numbers of 1.2 and 1.4. Moreover, it reveals the presence of three dominant modes, and the freestream Mach number strongly dictates the dominant mode that is driving the pressure field.

Shaking Tables Test on Seismic Responses of a Long-Span Rigid-Framed Bridge Considering Traveling Wave Effect and Soil–Structure Interaction

The traveling wave effect and soil–structure interaction have significant influence on the seismic response of large-span bridges with complex site conditions. In this paper, a 1/10 scaled-down large-span rigid-framed bridge model was designed and fabricated, and a shaking tables test considering the traveling wave effect and soil–structure interaction was carried out on a large-scale continuous rigid bridge model by a real-time substructure hybrid test technique. Influences of the traveling wave effect and soil–structure interaction on the seismic responses of the rigid-framed bridge specimen were systematically analyzed with experimental data. The test results showed that when the apparent wave speed was small, the traveling wave effect increased the seismic responses of the rigid-framed bridge. With the increase in apparent wave speed, the structural response under traveling wave excitation and uniform excitation was basically the same. The SSI effect lead to a great change in the seismic input peaks and spectral characters at the bottom of the pier, and increased the seismic responses of the rigid-framed bridge. When both traveling wave and the SSI effect were considered, there was a phase difference in the seismic excitation. The dynamic responses of a continuous rigid-framed bridge could not be simply obtained by superposition of the separate traveling wave effect or SSI effect. Meanwhile, the real-time substructure test method in this paper solved the problems that the traditional soil box experiment cannot be applied to the test of a large-scale model, the soil and bridge structure find it difficult to meet the unified similarity ratio, and the boundary conditions are difficult to simulate accurately.

Underwater advertisement call of the threatened Telmatobius rubigo (Anura: Telmatobiidae)

Abstract Underwater Passive Acoustic Monitoring (UPAM) has been used infrequently to register subsurface vocal behaviour in anurans. This study describes the underwater advertisement call of Telmatobius rubigo based on recordings made with UPAM technique. Telmatobius rubigo call is a low-frequency trill composed of 6 to 22 pulses with amplitude modulation. The spectral and temporal characters showed differences from other Telmatobius species. The UPAM, combined with automated call identification software, showed effectiveness in monitoring the calling behaviour of this aquatic Andean frog in their natural environment. UPAM and soundscape/riverscape analysis should be incorporated as a non-invasive tool for monitoring threatened aquatic species.

Finite element modeling of infrasound resonance in an underground tunnel structure

Recent observations of acoustic/infrasound signals emanating from an underground mine in central Utah show a spectral signature consisting of several dominant harmonics whose amplitude decay rate increases with frequency. This spectral character is consistent with a model in which the observed signals are generated from acoustic resonance within the mine tunnels. I present models of these signals computed using a discontinuous-Galerkin finite element formulation. The mesh geometry of these models is based on the known geometry of the mine tunnels obtained using traditional survey methods. Explosion source locations in the mine are known from previous analysis of seismic signals and operator logs and are associated with observations of infrasound resonance at multiple far-field stations. I explore the sensitivity of the modeled signals to changes in the source spectrum, boundary conditions within in the mine and perturbations to tunnel geometry. I discuss the possible application of my results to volcanic monitoring, industrial monitoring of underground structures, and the possible determination of underground tunnel geometries using far-field observations of acoustic resonance.

Temperature effect on spectral characters and dipole moment in short-lived excited singlet S1 state of 3HBI-7D-2HChromen-2-one laser dye in non-associative and highly viscous glycerol solvent

Steady state method is employed to study the effect of temperature on the absorption and emission characteristics of 3-(1H-benzo[d]imidazol-2-yl)-7-(diethylamino)-2H-chromen-2-one(3HBI-7D-2HChromen-2-one) laser dye in glycerol solvent. Temperature induces thermal effect on maxima absorption, emission wavelength, fluorescence intensity etc. Radiative and non-radiative transition probabilities mechanism, fluorescence lifetime, frequency assisted parameters decay rate constants, and activation energy is estimated. Advance thermochromic shift method is adopted to determine the ground and excited state dipole moments.

Development and evaluation of MWIR imaging spectrometer for multi-dimensional detection

For the detection of moving target in complex background, in order to increase the identification ability, the sensor needs the ability of multi-dimensional detection, not only image and spectrum, but also motion features. We propose a multi-slit imaging spectrometer, in which multiple slits instead of the single slit are arranged along the track on the focal plane of the fore-optics. Thus, the moving target is imaged with spectral resolution multiple times in one scanning period, which obtains the time resolution. We have developed a prototype with three slits covering spectrum between 3 µm and 5 µm. The prototype utilizes a reflective triple optics and a prism yielding a compact spectrometer design, which makes it much easier to realize the large field of view, the fast optical speed, the high optical transmission efficiency, the compact volume, and cooled opto-mechanics. Results of the laboratory tests verify the satisfaction of the imaging quality and spectral characters. The flight test shows this type of imaging spectrometers with multiple slits is feasible in the multi-dimensional detection of moving targets. It deserves the expected value in satellites and airborne applications in the future.

Design and Implementation of An Automated Car Plate Number Recognition System (ACPNRS)

The escalating global volume of vehicles on roadways necessitates innovative solutions for efficient traffic management, heightened security, and improved law enforcement. This research project centers on developing an Automated Car Plate Recognition System (ACPRS) to address these challenges. The ACPRS utilizes cutting-edge technologies in image processing, machine learning, and database integration for accurate and real-time license plate recognition. Beginning with an exploration of existing methodologies and technologies in the field, the research highlights their strengths and limitations. The conceptualization phase involves meticulous design, incorporating image preprocessing, license plate detection, character segmentation, optical character recognition (OCR), and database interaction. The research emphasizes the utilization of advanced image processing techniques, including deep learning algorithms, for robust license plate detection. Spectral analysis and character segmentation ensure reliable recognition in challenging conditions. OCR techniques enhance alphanumeric character interpretation, contributing to overall efficacy. The implementation phase involves software development, database setup, and integration with mobile applications for enhanced accessibility. Real-world applicability and scalability are pivotal considerations. The ACPRS is deployable in various contexts, such as parking management, security systems, and access control. Compatibility with mobile applications ensures widespread accessibility, broadening potential applications in diverse settings. Security and privacy measures include user authentication and data encryption to safeguard sensitive information. To validate the ACPRS’s effectiveness, comprehensive testing and evaluation use a diverse dataset. Real-world images, synthetic data, and publicly available datasets assess performance under different conditions. Evaluation metrics such as accuracy, speed, and robustness quantify capabilities and identify areas for improvement. In conclusion, this research project represents a significant contribution to automated vehicle identification. The proposed ACPRS, focusing on accuracy, real-time processing, and mobile accessibility, addresses critical challenges in traffic management, security, and law enforcement. Thorough exploration, design, implementation, and evaluation phases ensure understanding of the system’s capabilities and potential real-world applications. This work will be very significant to the developing country in managing their traffic and other related issues.

An unsplit-field viscoelastic complex-frequency-shifted perfectly matched layer for analysis of transient waves in heterogeneous media based on an efficient voxel element method

Wave propagation analysis of heterogeneous unbounded media employing domain discretization methods necessitates truncation of the finite computational domain at its truncation boundaries. The Perfectly Matched Layer (PML) is a robust absorbing boundary condition, which is extensively employed to favorably absorb outgoing scattered waves from the interior computational domain, regardless of frequencies and directions of outgoing waves. Nonetheless, most available PMLs are developed for elastic domains, while their developments in domain discretization methods, which consider damping using the Rayleigh damping formulation, are insufficient. In this study, a viscoelastic PML formulation is developed that accommodates the Rayleigh-type damping. The PMLs are basically developed from a coordinate transformation concept using a complex stretching function. Suitable stretching functions can efficiently control the absorptive properties and the spectral character of the PML. Besides, the stretching functions play a crucial role in the long-time stability of transient wave simulations. The standard stretching function usually results in spurious reflections, especially when propagating waves incident to the truncation boundary at near-grazing incidence. On the other hand, the complex-frequency-shifted (CFS) stretching function has been shown to mitigate long-time instability. Therefore, the proposed viscoelastic PML in the time-domain and frequency-domain are derived using the CFS stretching function for the first time. Comprehensive formulations of the proposed viscoelastic CFS-PML are given, where the displacement field is represented as the sole unknown variable of the problem. Hence, the proposed CFS-PML can be incorporated into any domain discretization method. However, the proposed CFS-PML is further developed in the context of the voxel element method, where element-by-element iterative strategies are implemented to solve the governing equations without storing global matrices in the computer memory. Comprehensive numerical experiments are conducted to demonstrate the validity and efficiency of the proposed viscoelastic CFS-PML formulation in analyzing soil profiles with various damping ratios and properties. Moreover, long-time stability for problems involving waveguides and near-grazing wave incidence is studied, where no instabilities are detected.

Ultrafast excited state dynamics of isocytosine unveiled by femtosecond broadband time-resolved spectroscopy combined with density functional theoretical study.

Isocytosine, having important applications in antivirus and drug development, is among the building blocks of Hachimoji nucleic acids. In this report, we present an investigation of the excited state dynamics of isocytosine in both protic and aprotic solvents, which was conducted by a combination of methods including steady-state spectroscopy, femtosecond broadband time-resolved fluorescence, and transient absorption. These methods were coupled with density functional and time-dependent density functional theory calculations. The results of our study provide the first direct evidence for a highly efficient nonradiative mechanism achieved through internal conversion from the ππ* state of the isocytosine keto-N(3)H form occurring within subpicoseconds and picoseconds following photo-excitation. Our study also unveils a crucial role of solvent, particularly solute-solvent hydrogen bonding, in determining the tautomeric composition and regulating the pathways and dynamics of the deactivation processes. The deactivation processes of isocytosine in the solvents examined are found to be distinct from those of cytosine and the case known for isocytosine in the gas phase mainly due to different tautomeric forms involved. Overall, our findings demonstrate the high photo-stability of isocytosine in the solution and showcase the remarkable effect of covalent modification in altering the spectral character and excited state dynamics of nucleobases.

Synthesis of Nanomagnetite/Crosslinked Carboxymethyl kappa Carrageenan Nickel Imprinted Composite

Nickel(II) ions are carcinogenic water pollutants. To increase the accuracy of instrumental analysis of Ni(II) content, several analytical preparation methods have been developed, including solid phase adsorption extraction. The development of magnetic solid phase extraction adsorbents for metal ions is required, to support the application of magnetic solid phase adsorption as a method of separating metal ions in aqueous samples. This research describes the synthesis of Magnetic Solid Phase Extraction adsorbents as Ni(II) ion adsorbents, nano magnetite/carboxymethyl kappa-carrageenan (CMKC) crosslinked bisphenol A diglycidyl ether (BADGE) imprinted Ni(II)-IIP ion composites. This research was carried out in several stages, synthesis and characterization of nano magnetite (NM), synthesis and characterization of CMKC, and synthesis of NM/CMKCNi(II)-IIP adsorbents. The results of the synthesis were analyzed for morphological characteristics, magnetic strength, spectral characteristics, crystallinity, and composition using SEM, FTIR, XRD, and XRF instruments. The adsorption ability of Ni(II) of the adsorbent was tested. Determination of Ni(II) ion content in the sample before and after adsorption was carried out using a flame atomic absorption spectrophotometer (FAAS). Based on the results of spectral character analysis, crystal diffraction patterns, magnetic strength, and morphology, it is confirmed that nano-magnetite has been successfully synthesized. The diameter of the nano magnetite grains is 21.8 nm, the adsorbent NM/CMKCNi(II)-IIP has magnetic properties and wavy surface morphology. The optimum adsorption ability of Ni(II) for the NM/CMKCNi(II)-IIP composite was 2.44 mg Ni(II)/g adsorbent. To evaluate the tendency of the adsorption ability of the adsorbent towards Ni(II) ions in the presence of competitor ions, the adsorption ability of the adsorbent to adsorp Ni(II) ions in samples containing Ni(II) ions, Pb(II) ions and a mixture of Ni(II) ions. and Pb(II) were determined, based on the results of the analysis, the ability of the adsorbent to adsorb Ni(II) ions was higher than the ability of the adsorbent to adsorb Pb(II) ions, in all types of samples.

In the Company of Specters: Forging Communal Unities in The Ministry of Utmost Happiness

This paper explores spectral characters marginalised on the basis of their social, religious, gender and ethnic labels in modern-day India, as depicted in Arundhati Roy’s The Ministry of Utmost Happiness. Using Jacques Derrida’s concept of hauntology, taken in terms of the fear of the original event repeating itself somewhere in the future as a specter, which in turn functions as a reminder of the responsibility that humanity has to resist different forms of injustices that surround us, I have analysed how Roy’s spectral characters, that is, characters who are out of place and linger across rigidly defined social categories, learn to forge unities amidst the communal divides of contemporary India under the wave of Hindutva. In the growing social fanaticism targeting different communities such as Dalits, Hijras and Muslims, spectral characters such as Musa, Saddam, Anjum and Tilo provide an alternative social consciousness against the backdrop of their chaotic socio-political environment which is a timely requirement in present-day India. Moreover, I have also inferred that the spectral landscapes in the novel, like the Khwabgah, Kashmir and the mall, remind the readers that the history of violence and injustice cannot be wiped away by reconstructing or destroying a physical space; they continue to haunt their surroundings both in the present and the future.
 Keywords: Hauntology, specters, landscape, alternative consciousness, India

Spectral and dynamical characters of 1D incommensurate optical lattices with [formula omitted]-symmetry

In this paper, we investigate the spectral and dynamical properties of a 1D incommensurate optical lattice, which displays a Parity-time (PT) symmetry described by the Non-Hermitian Aubry–André potential. We show through the spectral analysis of the eigenvalues and the associated eigenfunctions that, taking into account a non-Hermitian variant of the site energy modulated by a cosine form, leads the system to undergo a transition from the unbroken-PT phase to the broken-PT phase, which corresponds here to the delocalized-to-localized phase transition. Our findings also indicate that the critical point of transition can be selectively adjusted and consequently, the single-particle eigenstates taken in the metallic regime of the original Aubry–André model thus move from a conducting state to an insulating one upon an increase of the complex phase parameter. Furthermore, we also investigate the dynamical features of the system’s wave function according to different parameters.

Machine-learned dynamic disorder of electron transfer coupling.

Electron transfer (ET) is a fundamental process in chemistry and biochemistry, and electronic coupling is an important determinant of the rate of ET. However, the electronic coupling is sensitive to many nuclear degrees of freedom, particularly those involved in intermolecular movements, making its characterization challenging. As a result, dynamic disorder in electron transfer coupling has rarely been investigated, hindering our understanding of charge transport dynamics in complex chemical and biological systems. In this work, we employed molecular dynamic simulations and machine-learning models to study dynamic disorder in the coupling of hole transfer between neighboring ethylene and naphthalene dimer. Our results reveal that low-frequency modes dominate these dynamics, resulting primarily from intermolecular movements such as rotation and translation. Interestingly, we observed an increasing contribution of translational motion as temperature increased. Moreover, we found that coupling is sub-Ohmic in its spectral density character, with cut-off frequencies in the range of 102 cm-1. Machine-learning models allow direct study of dynamics of electronic coupling in charge transport with sufficient ensemble trajectories, providing further new insights into charge transporting dynamics.

Finite-dimensional representations of map superalgebras

We describe the block decomposition of the categories of finite-dimensional modules for classical map superalgebras and affine superalgebras in terms of spectral characters. En route to showing these block decompositions, we obtain a new description of finite-dimensional irreducible modules for classical map and affine superalgebras, provide formulas for their (super)characters and describe their extension groups. As an application, we establish a relation between the highest weights of a given finite-dimensional irreducible module for a classical map superalgebra with respect to non-conjugate Borel subalgebras.

Supramolecular self-assembly of carbon nanodots through edge functionalized interaction

Control of aggregation plays an important role in the photophysical behavior of luminescent nanomaterials. Herein, the concentration-dependent self-assembled hybrid of carbon nanodots (CDs) with the alteration spectral characters of H-/J-aggregation were observed. In detail, the CDs aging under different conditions presented obvious spectral variations ranging from visible to near-infrared regions, accompanied by the spontaneous evolution of nanoaggregates from CD nanoparticles. Theoretical calculations and experimental results confirmed the inhomogeneous surface functional groups could render CDs into nanoaggregates with the H- or J-aggregation through intraparticle or interparticle interaction, inducing the discrepant surface-confined charges in these intraparticle nanoaggregates and further contributing to their shift of absorption and emission bands. With the novel aggregation regulation, the CDs exhibited a tunable increase in their photothermal and photodynamic capability in comparison to their original counterparts. These findings shed a new light on the understanding of the photophysical behaviors for the self-assembled hybrid of CDs with the concept of supramolecular engineering.

Effects of nucleus rapher on the spectral character of electrical activity in the structures of the vision analyzer

Effects of nucleus rapher on the spectral character of electrical activity in the structures of the vision analyzer

Differences in the spectral characteristics of dissolved organic matter binding to Cu(II) in wetland soils with moisture gradients

The environmental behavior of heavy metals in soil is significantly regulated by their binding with dissolved organic matter (DOM), which is affected by soil moisture contents. However, the mechanism of this interaction in soils with varying moisture is still not well understood. Using a combination of ultrafiltration, Cu(II) titration, and multispectral (ultraviolet-visible absorption, 3D fluorescence, Fourier transform infrared) analysis techniques, we studied the differences in the spectral characteristics and Cu(II) binding properties of soil dissolved organic matter (DOM) and its different molecular weight (MW) fractions with moisture gradients. We found that the abundance and spectral characters of soil DOM changed with increasing soil moisture, i.e., the increase in abundance while the decrease in aromaticity and humification index. The components of DOM, shown by Fluorescence region-integration (FRI) analysis, also changed, with an increase in the proportion of protein-like substances and a decrease of humic-like and fulvic-like substances. The overall Cu(II) binding potential of soil DOM diminished with increasing soil moisture, as indicated by the fluorescence parallel factor (PARAFAC) analysis. This is aligns with the changes in DOM composition, as the humic-like and fulvic-like fractions exhibited higher Cu(II) binding potential compared to the protein-like fractions. The low MW fraction of the MW-fractionated samples showed a stronger binding potential for Cu(II) compared to the high MW fraction. Finally, the active binding site of Cu(II) in DOM, as revealed by UV-difference spectroscopy and 2D-FTIR-COS analysis, decreased with increasing soil moisture, with the order of preferentially functional groups shifting from OH, NH, and CO to CN and CO. This study emphasizes the impact of moisture variations on the characteristics of DOM and its interaction with Cu(II), providing insight into the environmental fate of heavy metal contaminants in soil in areas with alternating land and water conditions.

Application of wavy geometries for the reduction of trailing edge instability noise

Trailing edge instability noise can occur in a wide range of applications, including wind turbines and small aerial vehicles. It can be characterised by a high amplitude tonal or narrowband sound resulting from instability waves in the boundary layer scattering as they are convected over the trailing edge. In this study, a hybrid aero-acoustic model is used to demonstrate how wavy geometries can be used to successfully reduce trailing edge instability noise. The hybrid model uses incompressible large eddy simulations to compute acoustic source terms, which are then mapped onto a larger domain using radial basis functions. The acoustic perturbation equations are then solved on this larger domain to obtain the 3-dimensional acoustic field. The study uses a modified NACA0012 wing, where the surface contains spanwise waves of different wavelengths. The results show that there is an optimal wavelength that produces the greatest noise reduction for a given flow speed and Reynolds number, and that this relates to wavelengths of the dominant structures within the boundary layer. This shows that by understanding the spectral character of the boundary layer, one can design optimal geometries for reducing this important source of fluid-induced noise.

Study of the spectral characters–chlorophyll inversion model of Sabina vulgaris in the Mu Us Sandy Land

As the dominant shrub community plant in the Mu Us Sandy Land, S. vulgaris is the key factor of ecological environment restoration in the Mu Us Sandy Land, It is of great significance to explore the estimation and inversion of content based on spectrum for ecological environment evaluation and intervention in Mu Us Sandy Land. The SVC HR-1024 portable feature spectrometer and SPAD 502 chlorophyll meter were used to study Mu Us Sandy Land of S. vulgaris. The best band is screened by correlation matrix method, the best vegetation index is screened by Structural Equation Modeling model, and then the best inversion model is established by different mathematical modeling methods. Results revealed that the vegetation indices and chlorophyll content were correlated, combining the six vegetation indices revealed that 610–690nm and 700–940 nm were the bands with the highest correlation. In the selection of optimal vegetation index, NDVI, ratio vegetation index and mNDVI perform best and are suitable for subsequent modeling. Of the four models, the partial least squares model had the best fitting effect (R2 > 0.91). The univariate linear regression model had the simplest processing procedure, but its accuracy was unstable (R2 = 0.1–0.9). multivariate stepwise regression accuracy is also appropriate (R2 > 0.8). The stability of BP neural network modeling is not high. Compare the four methods, PLS and multivariate stepwise regression have their own advantages, and the accuracy is higher, you can make a choice according to the demand as the late modeling method.