Strong Oscillations Research Articles

In Silico modeling and exploration of new acceptor molecules with enhanced power conversion efficiency for high-performance organic solar cell applications

Developing an effective strategy to increase open circuit voltage with maximum PCE is vital to realizing high-performance OPVs (organic photovoltaic). In this report, a novel class of non-fullerene acceptor compounds has been constructed by us (D2APH1 to D2APH4) for high-performance OPVs. End-capped alterations of the JC2 (R) molecules were formed using capable end-capped units. A high Fill factor with FF% has been achieved with PCE of 30.34% for D2APH1 to D2APH4. Redshift and a limited energy band gap relative to the reference molecule, a change in the absorption spectra have been observed for D2APH1 to D2APH4. Further, designed molecules also expressed enhanced open-circuit voltage values and strong electron and hole mobility across metal electrodes. Easy exciton excitation inside an excited state is caused by low excitation energy and strong oscillation strength. The different geometric, photovoltaic, and optoelectronic analyses indicated that engineered molecules provide capable contributions to the creation of highly effective OPVs.

Sub-Seasonal Prediction of Sea-Gale Processes in the Yangtze River Estuary of China

The sea-gale process (SGP) is a significant and disastrous weather event for the marine industry. However, the sub-seasonal predictability of SGP remains unclear. In this study, we investigate the influence of low-frequency oscillation on SGP in the Yangtze River estuary from November to April, and its implications for sub-seasonal prediction. We noted that SGPs have a close relationship with the 10~30 day low-frequency component of the 10-m wind speed in the Yangtze River estuary, and typically occur during the peak phase of the low-frequency oscillation. The 10~30 day low-frequency oscillation of 10-m wind was found to be linked to the eastward propagation of extratropical Rossby waves from the North Atlantic across Europe to East Asia. This Rossby wave leads to the low-frequency oscillation of the Siberian high pressure and Japan Sea low pressure, which is indicative of the 10~30 day low-frequency oscillations of the 10-m wind speed in the Yangtze River Estuary. A sea-gale process index (SGPI) was constructed based on the low-frequency oscillation of the Siberian high and the Japan Sea low in order to predict SGPs at the sub-seasonal time scale. Hindcast and real-time forecasts showed that 2/3 of SGPs can be predicted with a leading time of 10~30 days, and that good sub-seasonal predictions of SGPs are connected with strong low-frequency oscillations at the initial forecast time. Therefore, SGPI can be adopted for the sub-seasonal prediction of SGPs in the Yangtze River Estuary.

Experimental and numerical simulation of shock train characteristics in an isolator with incident shocks

To better comprehend the steady-state structure and dynamic characteristics of shock train flow fields under interactions with incident shocks, wind tunnel experiments investigating the shock train flow fields in a supersonic isolator with incident shocks were conducted. High-speed schlieren visualization with multiple knife edges, surface tuft visualization, and high-frequency wall pressure measurements were used to analyze the shock train flow fields in the primary and corner regions. The understanding of the flow mechanism was enhanced based on additional three-dimensional steady numerical simulations. Flow field asymmetry was observed when the shock train interacted with parallel incident shocks. The shock train leading edge comprised a longer shock, which traversed the entire channel, and a shorter shock, with flow separation extending downstream of the longer shock. The flow downstream of the shorter shock passed through a small separation bubble before reattachment. The flow field was symmetrical when the shock train interacted with crossed incident shocks. Stronger oscillations were observed in the symmetric shock train owing to the adverse pressure gradient created by the incident shock and the inconsistent flow parameters downstream of the shock. The downstream propagation of the pressure fluctuation caused by the oscillation of the shock train leading edge was revealed based on coherence and phase analyses. The flow separation initiated further upstream in the corner region than in the primary region of the shock train flow field, and the separation flow covered a larger proportion of the flow field. These differences were enhanced by increasing the incoming Mach number.

Discretizing advection equations with rough velocity fields on non-Cartesian grids

We investigate the properties of discretizations of advection equations on non-Cartesian grids and graphs in general. Advection equations discretized on non-Cartesian grids have remained a long-standing challenge as the structure of the grid can lead to strong oscillations in the solution, even for otherwise constant velocity fields. We introduce a new method to track oscillations of the solution for rough velocity fields on any graph. The method in particular highlights some inherent structural conditions on the mesh for propagating regularity on solutions.

Quantum and Semiclassical Dynamics of Nonadiabatic Electronic Excitation of C(3P) to C1D) by Hyperthermal Collisions with N2.

The dynamics and kinetics of nonadiabatic excitation of C(3P) to C(1D) induced by hyperthermal collisions with N2 molecules are investigated using a quantum mechanical and two semiclassical nonadiabatic methods. The full-dimensional interaction potential energy surfaces and spin-orbit coupling, which facilitates the spin-forbidden process, are represented by a recently constructed diabatic potential energy matrix. The multistate quantum dynamics for selected partial waves found small transition probabilities due to the weak spin-orbit coupling. The spin-flip transition is the most favored near the threshold due to effective curve crossing. Strong oscillations are also found in the probabilities, which are attributable to resonances supported by the deep well in the singlet-state potential. Vibrational state-specified rate coefficients are reported from J-shifted quantum dynamics calculations, and they follow the Arrhenius form. Vibrational excitation in the N2 collision partner is found to increase the excitation rate at low temperatures, but the trend is reversed at high temperatures. The two semiclassical methods qualitatively reproduce the quantum rate coefficients.

Measuring the Quantum State of Dark Matter

AbstractIt is shown how the time series obtained from searches for ultralight bosonic dark matter (DM), such as the axion, can be used to determine whether it is in a coherent or incoherent quantum state. The example is essentially trivial, but it is hoped that explicitly addressing it will provoke experimental exploration. In the standard coherent state, oscillations in the number density occur over the coherence time, , where m is the particle mass and v is the galactic virial velocity, leading to a reduction in the constraining power of experiments operating on timescales , due to the unknown global phase. On the other hand, if the DM is incoherent then no such strong number oscillations occur since the ensemble average over particles in different streams gives an effective phase average. If an experiment detects a signal then the coherent or incoherent nature of DM can be determined by time series analysis over the coherence time. This finding is observationally relevant for DM masses, (corresponding to coherence times between a year and 100 s).

Intensity Modulation of Two Weakly Coupled Stimulated Oscillating Mechanical Modes in an Optomechanical Microbubble Resonator

We report that when two stimulating mechanical modes in an optomechanical microbubble resonator are weakly coupled to each other, strong oscillation intensity modulation occurs. The modulation was theoretically expected and experimentally observed. We theoretically derived the expressions of the coupling coefficient between the mechanical modes and calculated the region where weak coupling happens. We found that weak coupling exists when the optical quality factor of the microcavity is high and the detuning of the pump laser is close to the beat frequency of the two mechanical modes. Experimentally, we observed that when two mechanical modes are both in stimulated oscillation, they undergo strong intensity modulation as the optical pump power changes, and the coupling coefficient of the two modes is estimated to be 0.962 at the pump power when one mode is in the stimulated region and the other mode is at a stimulating threshold; this proves that the two mechanical modes are weakly coupled. Our results extended the weak coupling conclusion in multimode laser emission to stimulated oscillation in multiple mechanical modes.

Open-loop dynamic analysis of the catalytic oxidation of vocs with heat recovery

In this contribution, the open-loop dynamic behavior of the heat-integrated reactor for VOCs catalytic oxidation process is analyzed and the key variables that determine the stability of the system are studied. Systems with heat recovery often exhibit open-loop instability as a result of the positive heat feedback to the reactor. The results of the simulations demonstrate the existence of multiple steady states in the Reactor/FEHE/Furnace system, for the explored range of reactor inlet temperatures. There exists a close relation between the multiplicity of steady states and system stability for variables of interest such as feed fraction circulating through the FEHE and furnace duty. Under certain operating conditions, the system shows strong oscillations that can lead to physical damage to the catalyst (sintered) or undesired situations of light-off of the reactor. Particularly, sustained oscillations appear near the extinction point, an operating zone of practical interest to reduce the energy demand of the process and extend the catalyst life, since total conversion of VOCs is achieved at relatively low reactor inlet temperatures. The dynamic behavior of the reactor and heat exchanger in this steady state zones are analyzed. Finally, the effect of residence time and reactor time constant on system stability is discussed.

Electroencephalographic delta and alpha oscillations reveal phase-amplitude coupling in paediatric patients undergoing sevoflurane-based general anaesthesia

BackgroundSevoflurane-induced anaesthesia generates frontal alpha oscillations as early as 6 months of age, whereas strong delta oscillations are present at birth. In adults, delta oscillations and alpha oscillations are coupled: the phase of delta waves modulates the amplitude of alpha oscillations in a phenomenon known as phase-amplitude coupling. We hypothesise that delta-alpha phase-amplitude coupling exists in young children and is a feature of sevoflurane-based general anaesthesia distinct from emergence after anaesthesia. MethodsElectroencephalographic data from 31 paediatric patients aged 10 months to 3 yr undergoing elective surgery with sevoflurane-based anaesthesia were analysed retrospectively. Delta-alpha phase-amplitude coupling was evaluated during maintenance of anaesthesia and during emergence. ResultsDelta-alpha phase-amplitude coupling was observed in the study population. Strength of phase-amplitude coupling, represented by the delta-alpha mean amplitude vector, was greater during general anaesthesia than during emergence (Wilcoxon paired signed-rank test, Z=3.107, P=0.002). Frontal alpha amplitude during anaesthesia was not uniformly distributed across all delta phases. During general anaesthesia, alpha power was restricted to the positive phase of the delta wave (omnibus circular uniformity, general anaesthesia: P<0.001, mean phase: 114º; 99% confidence interval: 90º–139º; emergence: P=0.35, mean phase 181º, 99% confidence interval: 110º–253º). ConclusionsSevoflurane-based anaesthesia is associated with delta-alpha phase-amplitude coupling in paediatric patients. These findings improve our understanding of cortical dynamics in children undergoing general anaesthesia, which might improve paediatric intraoperative depth of anaesthesia monitoring techniques.

Phylogeography and introgression between Pinus kesiya and Pinus yunnanensis in Southeast Asia

AbstractSoutheast Asia (SEA) has seen strong climatic oscillations and fluctuations in sea levels during the Quaternary. The impact of past climate changes on the evolution and distribution of local flora in SEA is still poorly understood. Here we aim to infer how the Quaternary climate change affects the evolutionary process and range shifts in two pine species. We investigated the population genetic structure and diversity using cytoplasmic DNA markers, and performed ecological niche modeling to reconstruct the species past distribution and to project range shift under future climates. We found substantial gene flow across the continuous distribution of the subtropical Pinus yunnanensis. In contrast, the tropical Pinus kesiya showed a strong population structure in accordance with its disjunct distribution across montane islands in Indochina and the Philippines. A broad hybrid zone of the two species occurs in southern Yunnan. Asymmetric introgression from the two species was detected in this zone with dominant mitochondrial gene flow from P. yunnanensis and chloroplast gene flow from P. kesiya. The observed population structure suggests a typical postglaciation expansion in P. yunnanensis, and a glacial expansion and interglacial contraction in P. kesiya. Ecological niche modeling supports the inferred demographic history and predicts a decrease in range size for P. kesiya under future climates. Our results suggest that tropical pine species in SEA have undergone evolutionary trajectories different from high latitude species related to their Quaternary climate histories. We also illustrate the need for urgent conservation actions in this fragmented landscape.

On the quadratic wave equation with randomized oscillating coefficients

In this paper, we consider the asymptotic behavior of the solutions of the quadratic wave equations with perturbed oscillating coefficients which are very important mathematical models in describing the oscillation of particles imposed with time‐dependent electromagnetic fields. By the application of microlocal analysis and stochastic analysis, this paper makes a delicate classification of various types of time‐dependent oscillating coefficients on the principal quantum harmonic oscillator part and explores the corresponding regularity behavior and ‐estimates of the solution of the equation. It is interesting to find out that weak or mild oscillations will not cause any energy growth, while regular and strong oscillations will lead to polynomial or exponential growth of the energy. This is meaningful to help us explore the energy conversion mechanism in the electromagnetic field. Furthermore, in order to demonstrate the optimality of the ‐estimates, typical counterexamples with periodic coefficients will be constructed to show the lower bound of growth rate by the application of harmonic analysis and instability arguments. Compared with formal literatures focusing on the constant coefficients, current results in this paper reveal the essential relation between oscillation types and energy growth.

Heat transfer modulation in Rayleigh–Bénard convection by an oscillatory bottom plate

In this paper, we consider a heat transfer modulation in Rayleigh–Bénard convection by imposing a periodic sinusoidal oscillation to the bottom hot plate parallel to itself. Two-dimensional numerical simulations are carried out under lateral periodic conditions, over a Rayleigh number range of 106≤Ra≤109 and for a fixed Prandtl number of Pr = 7.1. For a given Rayleigh number, it is found that the Nusselt number, characterizing the global heat transfer efficiency of the system, shows a counter-intuitive initial drop and subsequent rise behavior, as the characteristic oscillatory velocity Vosc increases. Accordingly, taking the classical Rayleigh–Bénard convection as a reference, a heat transfer reduction regime for low Vosc and a heat transfer enhancement regime for high Vosc are recognized. The reduction regime is resulted from the thickening of the thermal boundary layer due to the amplified viscous effect by the oscillation, which increases the thermal resistance of the system. In addition to thickening the thermal boundary layer, a stronger oscillation could also trigger a thermal boundary layer instability, inducing massive emission of the thermal plumes and eventually giving rise to a significant global heat transfer enhancement. Moreover, the combined effect of thickening and destabilizing of the thermal boundary layer leads to a temporal periodic evolution of the Nusselt number at the bottom plate in the enhancement regime. A critical oscillatory velocity Vc is selected at the crossover between two regimes, and it is found decreasing with an increasing Ra as Vc∼Ra−0.2. Through dimensional analysis, we provide a physical explanation for this dependence.

On essential values of Sergeev's frequencies and exponents of oscillation for solutions of a third-order linear differential periodic equation

In this paper, we study various types of Sergeev's frequencies and exponents of oscillation for solutions of linear homogeneous differential equations with continuous bounded coefficients. For any preassigned natural number $N$, a periodic third-order linear differential equation is constructively built in this paper, which has the property that its upper and lower Sergeev frequency spectra of strict signs, zeros and roots, as well as the spectra of all upper and lower strong and weak oscillation indices of strict and non-strict signs, zeros, roots and hyperroots contain the same set, consisting of $N$ different essential values, both metrically and topologically. Moreover, all these values are implemented on the same set of solutions of the constructed equation, that is, for each solution from this set, all the frequencies listed above and the oscillation exponents coincide with each other. When constructing the indicated equation and proving the required results, analytical methods of the qualitative theory of differential equations were used, in particular, methods of the theory of perturbations of solutions of linear differential equations, as well as the author's technique for controlling the fundamental system of solutions of such equations in one particular case.

Three stages in the variation of the depth of hypoxia in the California Current System 2003–2020 by satellite estimation

The depth of hypoxia (DOH) is the shallowest depth at which the waters become hypoxic (oxygen concentration < 60 μmol kg−1), is a crucial indicator of the formation and expansion of oxygen minimum zones (OMZs). In this study, a nonlinear polynomial regression inversion model was developed to estimate the DOH in the California Current System (CCS), based on the dissolved oxygen profile detected by the Biogeochemical-Argo (BGC-Argo) float and remote sensing data. Satellite-derived net community production was used in the algorithm development, to denote the combined effect of phytoplankton photosynthesis and O2 consumption. Our model performs well, with a coefficient of determination of 0.82 and a root mean square error of 37.69 m (n = 80) from November 2012 to August 2016. Then, it was used to reconstruct the variation in satellite-derived DOH in the CCS from 2003 to 2020, and three stages of the DOH variation trend were identified. From 2003 to 2013, the DOH showed a significant shallowing trend due to the intense subsurface O2 consumption caused by strong phytoplankton production in the CCS coastal region. The trend was interrupted by two successive strong climate oscillation events from 2014 to 2016, which led to a significant deepening of the DOH and a slowing, or even reversal, of the variations in other environmental parameters. After 2017, the effects of climate oscillation events gradually disappeared, and the shallowing pattern in the DOH recovered slightly. However, by 2020, the DOH had not returned to the pre-2014 shallowing characteristic, which would lead to continuing complex ecosystem responses in the context of global warming. Based on the satellite inversion model of DOH in the CCS, we provide a new insight on the high-resolution spatiotemporal OMZ variations during an 18-year period in the CCS, which will aid in the evaluation and prediction of local ecosystems variation.

Flame Dynamics in the Combustion Chamber of Hybrid Rocket Using Multiangle Chemiluminescence

The flame dynamics in the combustion chamber of a hybrid rocket motor were visualized using novel chemiluminescence imaging. A multidirectional visualization system employing endoscopes generated images based on methylidyne chemiluminescence (CH*), with one endoscope in the precombustion chamber and two in the postcombustion chamber. Images were collected with a high-speed camera using a 1 ms exposure and a 1 kHz frame rate. Fuel grains having a helical or a conventional circular port structures were assessed, and combustion trials were conducted using a laboratory-scale hybrid rocket motor with oxygen as the oxidizer at mass flow rates from 10.43 to : equivalent to combustion chamber pressures ranging from 0.7 to 1.24 MPa. Flame structures were observed during the ignition, combustion, and shutdown stages; and the helical grain generated a larger, more intense flame zone. A proper orthogonal decomposition analysis showed that the helical grains also produced a greater degree of turbulence and stronger oscillations. These results confirm that a helical structure increases the flow turbulence and convective heat transfer in the combustion chamber. These effects lead to higher regression rates and better mixing efficiency that may, in turn, provide greater combustion efficiency at optimized oxidizer/fuel ratios.

Low frequency electrical waves in ensembles of proteinoid microspheres

Proteinoids (thermal proteins) are produced by heating amino acids to their melting point and initiation of polymerisation to produce polymeric chains. Amino acid-like molecules, or proteinoids, can condense at high temperatures to create aggregation structures called proteinoid microspheres, which have been reported to exhibit strong electrical oscillations. When the amino acids L-glutamic acid (L-Glu) and L-aspartic acid (L-Asp) were combined with electric fields of varying frequencies and intensities, electrical activity resulted. We recorded electrical activity of the proteinoid microspheres’ ensembles via a pair of differential electrodes. This is analogous to extracellular recording in physiology or EEG in neuroscience but at micro-level. We discovered that the ensembles produce spikes of electrical potential, an average duration of each spike is 26 min and average amplitude is 1 mV. The spikes are typically grouped in trains of two spikes. The electrical activity of the ensembles can be tuned by external stimulation because ensembles of proteinoid microspheres can generate and propagate electrical activity when exposed to electric fields.

Oil droplet spread on an immiscible surface of a vertically falling liquid film

Droplet spread over a vertically falling liquid film is studied in this paper. A simulation model is built and verified by experiment. Following this, a unique phenomenon that emerges in this context, namely, a strong inertial oscillation in an early stage of spreading, is analyzed. Finally, the equilibrium features of an oil droplet in this circumstance are discussed. The results show that the maximum spreading length in a strong inertial oscillation is much longer than the equilibrium length, being 152% the length of the latter in the base case. Furthermore, the equilibrium spreading length increases nearly linearly with the initial diameter of the droplet. The paper provides data to understand the effects of an oil droplet on a vertically falling film absorber to promote energy saving in a cold storage refrigeration system with low-grade heat.

Active stabilization of a pseudoheterodyne scattering scanning near field optical microscope.

Scattering scanning near-field optical microscopes (s-SNOMs) based on pseudoheterodyne detection and operating at ambient conditions typically suffer from instabilities related to the variable optical path length of the interferometer arms. These cause strong oscillations in the measured optical amplitude and phase comparable with those of the signal and, thus, resulting in dramatic artifacts. Besides hampering the comparison between the topography and the optical measurements, such oscillations may lead to misinterpretations of the physical phenomena occurring at the sample surface, especially for nanostructured materials. Here, we propose a stabilizing method based on interferometer phase control, which improves substantially the image quality and allows the correct extraction of optical phase and amplitude for both micro- and nanostructures. This stabilization method expands the measurement capabilities of s-SNOM to any slowly time-dependent phenomena that require long-term stability of the system. We envisage that active stabilization will increase the technological significance of s-SNOMs and will have far-reaching applications in the field of heat transfer and nanoelectronics.

Effect of Elastic Resonances of Substrate on Ferromagnetic Resonance in Yttrium Iron Garnet Films

The problem of excitation of ferromagnetic resonance in a thin ferrite film with magnetoelastic properties located on a thick elastic substrate is considered. A model is proposed for the excitation of elastic modes in the substrate due to the propagation of a periodic boundary regime created by magnetic oscillations in the film. The conditions for stationary oscillations are used to obtain the frequency response characteristics of ferromagnetic resonance, which exhibit strong oscillations due to the excitation of high-order elastic modes over the thickness of the substrate.

Formation of polar circumstellar discs in binary star systems

ABSTRACT We investigate the flow of material from highly misaligned and polar circumbinary discs that feed the formation of circumstellar discs around each binary component. With 3D hydrodynamic simulations we consider equal mass binaries with low eccentricity. We also simulate inclined test particles and highly misaligned circumstellar discs around one binary component for comparison. During Kozai–Lidov (KL) cycles, the circumstellar disc structure is altered through exchanges of disc eccentricity with disc tilt. Highly inclined circumstellar discs and test particles around individual binary components can experience very strong KL oscillations. The continuous accretion of highly misaligned material from the circumbinary disc allows the KL oscillations of circumstellar discs to be long-lived. In this process, the circumbinary material is continuously delivered with a high inclination to the lower inclination circumstellar discs. We find that the simulation resolution is important for modelling the longevity of the KL oscillations. An initially polar circumbinary disc forms nearly polar, circumstellar discs that undergo KL cycles. The gas steams accreting onto the polar circumstellar discs vary in tilt during each binary orbital period, which determines how much material is accreted onto the discs. The long-lived KL cycles in polar circumstellar discs may lead to the formation of polar S-type planets in binary star systems.