Apparent Frequency Research Articles

Studies of Kinetics and Non-Isothermal Decomposition of Synthesized Novel Organic Terpolymer Resin

Abstract: The terpolymer resin 2,4-DHP-4-PAF-III was prepared by condensation of 2,4-dihydroxypropiophenone, 4- pyridylamine and formaldehyde in the presence of 2M hydrochloric acid as a catalyst in the temperature range 125 ± 2 0C for 5 hrs in 3:1:5 molar ratios of reactants. Elemental analysis, FT-IR, and 1H-NMR spectral studies have been carried out to confirm the structure of the resin. The thermal degradation behavior of terpolymer was studied using thermogravimetric analysis (TGA) in air atmosphere at a heating rate of 10 0C/min. Sharp-Wentworth and Freeman-Carroll methods were used to calculate thermal activation energy (Ea), entropy change (∆S), free energy change (∆F), apparent entropy change (S*), frequency factor (Z) and order of reaction (n). Thermal activation energy (Ea) calculated by Sharp-Wentworth (28.81 KJ/mole) method and Freeman-Carroll (29.47 KJ/mole) method are in good agreement.

Performance of an oscillating water column wave energy converter device under random ocean waves and ocean currents

The present study investigates the hydrodynamic performance of an onshore oscillating water column (OWC) device placed over an undulated bottom topography by analyzing its hydrodynamic efficiency under the action of combined wave–current interaction. The classical small-amplitude water wave theory is used to model the physical problem. The constant boundary element method is employed to solve the boundary value problem. Significant attention is devoted to describing the hydrodynamic parameters associated with the OWC device by considering the mutual combination of the random waves and ocean currents in the wave propagation phenomena. To examine the complex dynamics of the combined irregular wave current phenomena, the Det Norske Veritas spectrum accompanied by a suitable sea state has been considered for the present study. Considering the existence of opposing and following currents in wave propagation, a comprehensive analysis is conducted on the interactions of regular and irregular water waves with the OWC device. The simulated results demonstrate that the presence of ocean currents in the wave propagation phenomenon strongly influences the resonating patterns of the efficiency and force curves. Additionally, the Doppler shift in the apparent frequency caused by the following currents in the random wave–current interaction significantly improves the device's efficiency for an appropriate structural design.

Low-temperature sintering BCZT-Dy ceramics with low strain hysteresis for actuator application

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

Kinetic analysis of dehydration/dehydroxylation from carbonaceous chondrites by in situ heating experiments under an infrared microscope

AbstractCI, CM, and CR carbonaceous chondrites contain hydrous minerals, indicating that their parent bodies underwent aqueous alteration at low temperatures. Some of these chondrites, such as heated CM, CI, and CY chondrites, experienced thermal dehydration by impacts or solar radiation after aqueous alteration. This study conducted heating experiments on carbonaceous chondrites and evaluated their dehydration/dehydroxylation kinetics in an effort to explain the thermal history of the parent asteroids of heated carbonaceous chondrites using their degrees of dehydration/dehydroxylation of hydrous minerals. Murchison (CM2.5) and Ivuna (CI1), relatively primitive (having not undergone thermal alteration) carbonaceous chondrites, were used as starting materials. Weakening in the OH band at ~3680 cm−1 (2.72 μm) with isothermal heating at 350–500°C (Murchison) and 450–525°C (Ivuna) were observed under in situ infrared spectroscopy (FT‐IR) equipped with a heating stage. To determine the rate constants, the decrease in the OH band was fitted using kinetic models such as first‐order reactions, two‐dimensional diffusion, and three‐dimensional diffusion. The apparent activation energies and frequency factors were determined using the Arrhenius equation. Time–temperature transformation diagrams were drawn to represent the decrease in the OH‐band intensity as a function of temperature and heating duration. Such kinetic approaches can provide constraints on the temperature and time of the dehydration/dehydroxylation processes and enable us to estimate long‐term effects from experiments in the laboratory within a short time.

Detecting the heterodyning of gravitational waves

Abstract Gravitational waves modulate the apparent frequencies of other periodic signals. Low-frequency gravitational waves could therefore be detected by observing frequency modulations in signals from higher-frequency sources, e.g. those from binary white dwarfs detected with the LISA gravitational-wave detector. We propose a concrete method to extract these modulations by coherently adding the cross-spectra of a large number of well-resolved quasi-monochromatic signals. We apply this method to the case of LISA, and find this method would enable the detection of background gravitational wave strain amplitudes of, e.g. A ≃ 10 − 10 at a frequency F ≃ 10 − 8 Hz , given current projections for the number and properties of Galactic binary white dwarfs and the sensitivity of the instrument. We also estimate (to within an order of magnitude) that this method could potentially compete with that of current pulsar timing arrays when using signals from binary neutron stars such as those expected to be observed with proposed detectors like DECIGO. Our results show that gravitational-wave detectors could be sensitive at frequencies outside of their designed bandwidth using the same infrastructure, which has the potential to open up unexplored and otherwise inaccessible parts of the gravitational wave spectrum.

Kinetics study on the low-temperature soda roasting of boron-rich blast furnace slag

The method of preparing borax by low-temperature soda roasting and water leaching of boron-rich blast furnace slag (BRBFS) is a novel method for extracting boron from BRBFS. In order to further improve the water leaching rate of boron, this article mainly studied the low-temperature soda roasting kinetics of BRBFS. The effects of roasting temperature and Na2CO3 addition on the water leaching rate of boron were investigated. The results demonstrate that when the amount of Na2CO3 added is four times of the theoretical amount, the kinetics of NaBO2 formation can be described by the Nucleation (Avrami) model in the temperature range of 600–700 °C. The corresponding apparent activation energy is 54.45 kJ/mol, and the apparent frequency factor is 215.16 h−1. It was found that at a roasting temperature of 700 °C,when the amount of sodium carbonate added is twice, three times, and four times of the theoretical amount, the kinetics of NaBO2 formation matches with 3-D Diffusion (Jander) model, Nucleation and Growth (Avrami-Erofeev) model, and Nucleation (Avrami) model, respectively. With an increase in the amount of Na2CO3 added, the rate-controlling step for the formation of NaBO2 transitions from being diffusion-controlled to nucleation-controlled.

Unifying the temperature dependent dynamics of glass formers.

Strong changes in bulk properties, such as modulus and viscosity, are observed near the glass transition temperature, Tg, of amorphous materials. For more than a century, intense efforts have been made to define a microscopic origin for these macroscopic changes in properties. Using transition state theory (TST), we delve into the atomic/molecular level picture of how microscopic localized unit relaxations, or "cage rattles," evolve to macroscopic structural relaxations above Tg. Unit motion is broken down into two populations: (1) simultaneous rearrangement occurs among a critical number of units, nα, which ranges from 1 to 4, allowing a systematic classification of glass formers, GFs, that is compared to fragility; and (2) near Tg, adjacent units provide additional free volume for rearrangement, not simultaneously, but within the "primitive" lifetime, τ1, of one unit rattling in its cage. Relaxation maps illustrate how Johari-Goldstein β-relaxations stem from the rattle of nα units. We analyzed a wide variety of glassy materials and materials with a glassy response using literature data. Our four-parameter equation fits "strong" and "weak" GFs over the entire range of temperatures and also extends to other glassy systems, such as ion-transporting polymers and ferroelectric relaxors. The role of activation entropy in boosting preexponential factors to high "unphysical" apparent frequencies is discussed. Enthalpy-entropy compensation is clearly illustrated using the TST approach.

The role of the foundation flexibility on the seismic response of a modern tall building: Vertically incident plane waves

The soil-structure interaction (SSI) is an integral part of the seismic response of structures. The knowledge about its effects is based largely on numerical simulations involving simplified models. In this paper, we examine the consequence of several assumptions in SSI models of buildings, with emphasis on the rigid foundation assumption. To this end, we analyze several variants of a linear three-dimensional finite element model of the structure and soil corresponding to a uniquely instrumented 50-story skyscraper, with a basement on a pile foundation, located in southwest China. The models are excited by triaxial motion due to a vertically incident plane wave. The most realistic model (with basement and piles, both with bond contact with the soil), predicted an 8 % reduction of the apparent frequency and a 30 %–50 % increase in the apparent damping ratio of the 1st mode of vibration, relative to the model with fixed basement. The model with a rigid foundation (basement) embedded in the soil underestimated the reduction in apparent frequency by a factor of two. The SSI effects were the most pronounced for the model with flexible basement and no piles (16 %–19 % reduction in apparent frequency and 73 %–86 % increase in apparent damping ratio). The basement-structure interaction reduced the apparent frequency by 5 %–8 % depending on the direction. It is concluded that, for such a building, a detailed model of the structure and its foundation is needed to predict reliably the SSI effects.

A modified linear-elastic model for calibration of resonant column devices accommodating drive system compliance

Measurements of small-strain shear modulus of soils and rocks using the resonant column apparatus are highly dependent on accurate physical characterisation of the apparatus's drive components. This is typically achieved by way of a calibration exercise, yet it is widely reported that existing interpretation methods yield physical properties that vary with frequency, complicating subsequent interpretation of test data. Previous research has indicated that much of this apparent frequency dependency occurs due to compliance of the drive system. In this study the linear elastic model of the resonant column apparatus is adapted to include a new drive stiffness parameter, supported by finite-element analysis of the drive system. A novel calibration method is presented based on this drive compliance model. Thirteen calibration bars and three added masses are used to conduct an extensive calibration exercise for both a Hardin- and Stokoe-type resonant column apparatus. The novel calibration method is compared with three existing methods in the literature. Limitations of the four methods are identified and discussed. The drive compliance model and its associated calibration method is shown to be a robust means of characterising the apparatus behaviour while successfully eliminating frequency dependency of the calibration parameters. The model is valid where total system damping is small and is particularly valuable when testing stiff specimens where common apparatus assumptions may not apply.

Observation of dense collisional soliton complexes in a two-component Bose-Einstein condensate

Solitons are nonlinear solitary waves which maintain their shape over time and through collisions, occurring in a variety of nonlinear media from plasmas to optics. We present an experimental and theoretical study of hydrodynamic phenomena in a two-component atomic Bose-Einstein condensate where a soliton array emerges from the imprinting of a periodic spin pattern by a microwave pulse-based winding technique. We observe the ensuing dynamics which include shape deformations, the emergence of dark-antidark solitons, apparent spatial frequency tripling, and decay and revival of contrast related to soliton collisions. For the densest arrays, we obtain soliton complexes where solitons undergo continued collisions for long evolution times providing an avenue towards the investigation of soliton gases in atomic condensates.

Cis-trans adsorption configuration influenced high-efficient hydrogenation of furfural over zeolite-encapsulated PtCu bimetallic catalyst

Bimetallic catalysts are promising materials for high-efficient conversion of lignocellulose to value-added chemicals, but synthetic methods with reasonable generality are still lacking. Herein, we report a novel method for synthesizing bimetallic catalyst PtCu@S-1(S-1, silicalite‑1) via zeolite encapsulation with the aid of protecting chelating ligands. PtCu@S-1 displays remarkable activity for the hydrogenation of furfural (FUR) to furfuryl alcohol (FOL), and its apparent turnover frequency (TOF) values reach up to 735 mmolFUR·mmolPt−1·h−1 and 88 mmolFUR·mmolCu−1·h−1, which are ∼ 16 and ∼ 4 times higher than that of Pt@S-1 and Cu@S-1. Interestingly, we for the first time find that OO-trans FUR is a preferable adsorption configuration over OO-cis FUR on PtCu@S-1 due to the Pt sites coordinating with the carbon atom on the furan ring. More importantly, the adsorption ability of OO-trans FUR is stronger than that of OO-cis FUR, which increases the concentration of adsorbed species on PtCu@S-1 and accelerates the hydrogenation of FUR.

Thin reservoir prediction technology with sensitive parameters of tight gas in southwest Ordos Basin

In the southwest of Ordos Basin, the loess layer is very thick, the surface elevation changes rapidly, and the near-surface low-velocity zone velocity changes greatly in vertical and horizontal directions, resulting in prominent static correction problems. Affected by the strong absorption of the loess layer, the effective frequency band of the original data is narrow, the apparent main frequency is low, and the "double high" processing is difficult. The reservoirs of He-8 and Shan-1 are deep-buried, thin and dense, and their lateral changes are fast. In this paper, the sensitive data of "two widths and one height" 3D seismic is optimized to obtain high-quality sensitive data. The sensitive orientation is optimized by combining drilling data, and the sensitive parameter based on pre-stack inversion technology is adopted to improve the prediction accuracy of thin reservoirs. The new Chengtan-3-Long19 He-8 sand belt was discovered, the well location deployment plan was optimized, the efficient drilling of horizontal Wells was supported and the fracturing plan was optimized. 26 well locations were deployed using 3D seismic, 11 were completed drilling, and 9 were class I + II, an increase of 30% compared with 2D seismic.

On the origin of the Ponzo illusion: An attentional account.

The Ponzo illusion is a famous optical illusion that is not well understood so far. Here we suggest that its origin is closely linked to distribution of spatial attention. In essence, it arises because the size of the attentional field varies between different parts of the stimulus layout, which comes with different spatial resolution and, as a consequence, different apparent sizes of the objects in the stimulus display. We report four experiments (conducted in 2022 and 2023), which support this approach. The illusion substantially decreases when the stimulus layout is modified so that the size of the supposed attentional field is equalized for the crucial parts (Experiment 1). Moreover, we induce a Ponzo-like illusion by means of attentional cues only (Experiment 2). The perceived spatial frequency differs for different parts of the stimulus layout consistent with predicted changes in spatial resolution (Experiment 3). Attentional cuing exerts an analogous influence on the apparent spatial frequency (Experiment 4). The presented approach provides a novel look at the origin of the Ponzo illusion and related phenomena. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Flexible Double‐Layer Adjustable Frequency Selective Surfaces Based on 3D Cross‐Shaped Kirigami Structure

AbstractFrequency‐selective surfaces (FSS) with flexible treatment can be employed in various applications. This paper develops a mechanically constructed flexible double‐layer adjustable FSS based on a 3D cross‐shaped kirigami structure design. Through mechanical stretching, the kirigami structure partly adhered to the ecoflex substrate enables this FSS to modulate the resonant frequencies of two filter bands synchronously. Meanwhile, the structural deformation triggered by mechanical stretching may function as a switch to adjust the filter band with a higher resonant frequency. According to the results of EM experiments and simulations, in the absence of stretching, the undeformed FSS with a double‐layer structure has two filter bands. Compared to the undeformed configuration, the stretching induces structural deformation, which results in apparent resonant frequency shifts of both the two filter bands and the contraction of the filter band with higher resonant frequency. A buckling model that has been theoretically, cumulatively, and experimentally proven is utilized to investigate the structural deformation of this FSS caused by stretching. It is convenient to switch flexible double‐layer adjustable FSS' deformation by mechanical method. This flexible double‐layer adjustable FSS offers a new design strategy for the application of FSS, paving the route for new developments in electromagnetic compatibility.

Deciphering the mechanistic insights of 4-nitrophenol reduction catalyzed by a 1D-2D Bi2S3 nanostructured catalyst.

Exploring the reaction mechanism and the role of a catalyst in the conversion of pollutants to value-added products is vital for sustainable development. Herein, a polyvinylpyrrolidone-assisted liquid-phase reflux strategy was utilized to synthesize anisotropic 1D-2D Bi2S3 nanostructures. The as-synthesized nanostructures were used as catalysts in batch experiments for 4-nitrophenol (4-NP) reduction and they exhibited an apparent rate constant (kapp), turnover frequency (TOF), and activation energy (Ea) of 0.441 min-1, 1.543 h-1 and 26.13 kJ mol-1, respectively. Also, the effects of catalyst dosage, NaBH4 amount, 4-NP concentration, solvents, pH, and common ions were evaluated. Isotope labeling and kinetic isotope effects (KIEs) confirm that water is the proton source in 4-NP reduction. Electrochemical studies revealed that the nanostructured 1D-2D Bi2S3 enables the dissociation of BH4- into active absorbed and adsorbed hydrogen () species and assists in the catalytic reduction of 4-NP. This study offers a new insight into designing an efficient nanostructured 1D-2D Bi2S3 catalyst for 4-nitrophenol reduction.

The two faces of secondary contact on islands: Introgressive hybridization between endemics and reproductive interference between endemics and introduced species

AbstractAimHybridization is thought to have played an important role in shaping the evolutionary history of diverse island taxa. Here, we propose an ecological and evolutionary framework for understanding the causes and consequences of heterospecific mating on islands—with and without introgressive hybridization. We use this framework to support our main contention that cases of secondary contact among endemic species should commonly result in introgressive hybridization whereas cases of contact between endemic and introduced species should commonly result in reproductive interference (RIN)—resulting in two qualitatively different faces of secondary contact on islands.LocationCanary Islands, Galapagos, New Zealand, Caribbean and Hawaii.Taxa705 vertebrate, invertebrate and plant species spanning 167 genera and 99 families.MethodsUsing a quantitative analysis of empirical research on secondary contact on islands, we weigh evidence for the causes and consequences of secondary contact and heterospecific mating on islands. In particular, we compare cases of secondary contact between endemic species versus secondary contact between endemic and introduced species.ResultsWe find that the drivers of secondary contact and heterospecific mating on islands most frequently reported in the literature are disturbance, long‐distance (e.g. inter‐island) dispersal and compromised assortative mating. We find support for the hypothesis that extensive introgression is a more common outcome between endemic species while RIN is a more common outcome between endemic and introduced species.Main ConclusionsWe conclude that there are biological reasons to predict secondary contact and heterospecific mating to be common on islands for all taxa, but that the consequence of secondary contact is categorically different for contact between endemic species and contact between endemic and introduced species. We conclude that the former likely explains the apparent frequency of hybridization on islands, while the latter presents a cryptic and underappreciated conservation threat.

Distinguishing Electromagnetic Ion Cyclotron (EMIC) Waves From Other Pc1 Signatures in Satellite Recordings by Means of the Swarm Satellite Constellation

AbstractIn this study we make use of the closely spaced Swarm A and C spacecraft to determine the main wave parameters of micro‐pulsation in the Pc1 range. Generally, the interpretation of wave events in satellite recordings suffers from the spatial/temporal ambiguity of such data. To resolve that problem, we use for the first time in the 0.2–5 Hz apparent frequency range high‐resolution magnetic field data from the Swarm A/C spacecraft pair. Particularly suitable for this analysis is the period of Counter Rotating Orbit Phase in 2021. During that period the along‐track distance between the spacecraft was varied from 2 to 40 s. Surprisingly many of the wavy signals at middle latitudes were identified as small‐scale (order of 10s km) quasi‐static field‐aligned current (FAC) structures. Some of the events turned out to be medium‐scale (100–200 km) waves oscillating at 1 Hz or less. A number of published electromagnetic ion cyclotron (EMIC) waves were checked on their consistency. One characteristic is their long wavelength (∼1,000 km). About half of the cases passed the check, the other did not satisfy the spatial homogeneity. The small‐scale FAC structures we believe to be driven by atmospheric gravity waves. While the medium‐scale waves we prefer to relate to the effects of the ionospheric Alfvén resonator.

Preliminary study to scale up microbubble generation with acoustic wave

This research focuses on the utilization of acoustic wave to control the generation of microbubbles from a capillary tube, aiming for mass production with porous media. Initially. ultrasonic standing wave is employed to generate small-size microbubble since high amplitude is required for the pipette with smaller pore size which has high resistance. However, for large bubble generation, secondary acoustic radiation force between bubbles is increased and induces bubble coalescence. Pulsing wave can reduce the force strength by reducing wave cycles (apparent frequency) and increasing the distance between bubbles by controlling bubble generation frequency. Finally, maximum bubble generation frequency is calculated at each bubble size based on calculation of limiting factors such as gas permeability and secondary acoustic radiation force. The research will contribute to generate wide size range of multiple bubbles in aqueous solution and set up its limitation regarding bubble generation frequency through theoretical calculation. The data will be utilized for multiple bubble generation with porous media.

Revealing the effect of phase and time coupling on NMR relaxation rate by random walks in phase space.

Phase-time coupling is a natural process in the phase random walks of a spin system; however, its effect on the nuclear magnetic resonance (NMR) relaxation is a challenge to the established theories such as the second-order quantum perturbation theory. This paper extends the recently developed phase diffusion method to treat the phase-time coupling effect, based on uncoupled phase diffusions, and coupled random walks. The instantaneous projection of the rotating random field is employed to get the accumulated phase of the NMR observable. In the static frame and the rotating frame, the phase diffusion coefficients are derived. The obtained theoretical results show that the phase-time coupling has a significant impact on the NMR relaxation rate: The angular frequency ω in the spectral density is modified to an apparent angular frequency ηω, where η is the phase-time coupling constant. The strongest coupling has η equaling 2, while η equaling 1 corresponds to the traditional results. As an example, the modified relaxation time expressions based on both monoexponential and nonmonoexponential functions can successfully fit the previously reported ^{13}CT_{1} NMR experimental data of polyisobutylene (PIB) in the blend of PIB and head-to-head poly(propylene). In contrast, the traditional relaxation rate expression based on the monoexponential time correlation function cannot fit such experimental data. With the phase-time coupling, the obtained characteristic time of the segmental motion is faster than that from conventional results.

Catalytic two-dimensional Pd decorated graphene oxide membrane for efficient 4-nitrophenol reduction

Catalytic Pd decorated graphene oxide (Pd/GO) membrane with efficient catalytic activity was developed by in-situ reduction of Pd2+ on GO nanosheets followed by vacuum filtration. A high 4-nitrophenol (4-NP) reduction efficiency was achieved by using the Pd/GO catalytic membrane with layered structure because of evenly distribution of Pd nanoparticles (NPs) in the interlayer space of GO membrane, ensuring sufficient contact between 4-NP molecules and Pd NPs. The apparent kinetic rate constant and turnover frequency (TOF) reached to 138.4 s−1 and 813 h−1 under a continuous-flow system using 4000 mg/L of 4-NP at 20 °C. During a 300 min of continuous-flow catalysis, the 4-NP conversion was kept above 98% at 20 °C. This high catalytic efficiency of the Pd/GO catalytic membrane under high 4-NP concentration and continuous-flow catalysis made it promising and competitive in the application of catalytic membrane for efficient catalytic process.