Intense Energy Transfer Research Articles

Near- and Superinertial Internal Wave Responses and the Associated Energy Transfer after the Passage of Tropical Cyclone Fitow at a Midlatitude Shelf Slope

Abstract Observations from a mooring station at the East China Sea (ECS) shelf slope revealed both near- and superinertial dynamic responses to tropical cyclone (TC) Fitow. Different from the typical near-inertial response, near-inertial internal waves (NIWs) after TC Fitow showed a complicated phase pattern due to its superposition with parametric subharmonic instability (PSI)-generated M1 subharmonic waves. The wind-injected near-inertial kinetic energy (NIKE) was largely restrained to the upper 250 m. Wave packet analysis revealed the co-occurrence of enhanced NIKE, circularly polarized near-inertial currents, veering NIW propagation direction, and shrinking NIW vertical wavenumber at the base of the Kuroshio (∼180 m). This indicated the trapping and stalling of the TC-generated NIWs. Intense high-frequency internal waves (HFIWs) appeared immediately after TC Fitow which had an average period of ∼24 min and lasted ∼8 h. HFIWs also existed before the arrival of TC Fitow with a regular semidiurnal cycle. However, the HFIW after TC did not follow the semidiurnal cycle and had much larger amplitudes and longer-lasting periods. Local generation of supercritical flow over a slope or evolution from propagating internal tide as modified by TC may have induced these HFIWs. Along with the occurrence of intense HFIWs after TC Fitow, intense energy transfers from NIWs to HFIWs were identified. Due to the limited vertical propagation of TC-induced NIWs, it was the PSI-generated M1 subharmonic wave rather than the wind-induced NIW that contributed most to the energy transfer. Significance Statement Winds blowing over the ocean generate not only surface waves but also another type, so-called internal waves, which can travel down into the ocean. These internal waves carry a large amount of wind-injected energy into the ocean interior and are thought to play an important role in sustaining ocean turbulent mixing and circulation. We provided evidence that the passage of a tropical cyclone (TC) can induce different types of internal wave responses: near-inertial and high-frequency internal waves. Interactions and energy transfer between different internal waves occurred. With the TC-induced near-inertial internal waves trapped in the upper ocean, the background M1 subharmonic waves contributed most to the interactions with high-frequency internal waves. This fact is crucial in understanding the propagation and dissipation of wind-injected energy in the ocean, which plays an important role in controlling the ocean interior mixing and large-scale circulation.

Ce/Mn/Cr: (Re,Y)3Al5O12 Phosphor Ceramics (Re = Gd, Tb and Lu) for White LED Lighting with Significant Spectral Redshift and Improved Color-Rendering Index.

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y0.997-xRexCe0.003)3(Al0.9748 Mn2+0.024Cr3+0.0012)5O12(Rex = 0, Gd0.333, Gd0.666, Gd0.997, Tb0.333, Tb0.666, Tb0.997 and Lu0.997 were prepared by solid-state reaction and vacuum sintering, and exhibited potential for high-quality, solid-state lighting. Doping with Cr3+ and Mn2+ effectively enhanced the red component of Ce3+ spectra through the intense energy transfer from Ce3+ ions to Mn2+/Cr3+ ions. The crystal field splitting of [GdO8] and [TbO8] was more extensive than that of [YO8], causing a massive redshift in the Ce3+ emission peaks from 542 to 561 and 595 nm, while [LuO8] had an opposite effect and caused a blueshift with a peak position at 512 nm. White LED devices incorporating Ce/Mn/Cr: (Gd0.333Y0.664)3Al5O12 phosphor ceramic exhibited a high CRI of 83.97, highlighting the potential for enhancing the red-light component of white LED lighting.

Energy transfer and vortex structures: visualizing the incompressible turbulent energy cascade

The transfer of kinetic energy from large to small scales is a hallmark of turbulent flows. Yet, a precise mechanistic description of this transfer, which is expected to occur via an energy cascade, is still missing. Several conceptually simple configurations with vortex tubes have been proposed as a testing ground to understand the energy cascade. Here, we focus on incompressible flows and compare the energy transfer occurring in a statistically steady homogeneous isotropic turbulent (HIT) flow with the generation of fine-scale motions in configurations involving vortex tubes. We start by filtering the velocity field in bands of wavenumbers distributed logarithmically, which allows us to study energy transfer in Fourier space and also visualize the energy cascade in real space. In the case of a statistically steady HIT flow at a moderate Reynolds number, our numerical results do not reveal any significant correlation between regions of intense energy transfers and vorticity or strain, filtered in corresponding wavenumber bands, nor any simple self-similar process. In comparison, in the transient turbulent flow obtained from the interaction between two antiparallel vortex tubes, we observe a qualitatively simpler organization of the intense structures, as well as of the energy transfer. However, the correlations between energy transfer and strain are small, and point to complicated dynamics of energy transfer. By imposing a structure at large scales consisting of antiparallel vortex tubes in a statistically steady flow, we observed a picture qualitatively similar to what was observed for the transient flow, but the energy transfer statistics do not reproduce the type of triadic interactions seen in HIT. These results indicate that the specific properties of the large-scale vortical structures affect the way energy is transferred, and may not be fully representative of HIT.

Luminescence Studies on Dy3+ Doped Calcium Aluminum Borosilicate (CABS) Glasses for White Light Emission and Applications in w-LEDs.

Dy3+ doped calcium aluminum borosilicate (CABS) glasses have been synthesized via quick melt quench technique. CABS: xDy3+ glasses (x = 0.1, 0.5, 1, 1.5 and 2mol%) were subjected to various morphological and photoluminescence studies. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to study the structural and bonding nature of the undoped glass. The excitation spectra of Dy3+ doped CABS glasses under 574nm emission show many sharp peaks amongst which the transition from 6H15/2 → 6P7/2 (351nm) had the highest intensity. Under 351nm excitation, glasses exhibit sharp peaks in the blue, yellow and red regions corresponding to the transitions 4F9/2 → 6H15/2, 6H13/2, 6H11/2 and 6H9/2 respectively. The dipole-dipole nature of the interaction between the Dy3+ ions is confirmed via Dexter theory and Inokuti-Hirayama (I-H) model. CIE coordinates estimated from the emission profiles of these glasses under 351nm excitation fall in the white region. Considering that these glasses exhibit sharp visible emission under UV excitation, have stable yellow to blue (Y/B) ratios and fast decays with intense energy transfers, we propose to utilise these glasses for white light generation and other white light LED (w-LED) and solid-state lighting (SSL) applications.

Subion-Scale Turbulence Driven by Magnetic Reconnection.

The interplay between plasma turbulence and magnetic reconnection remains an unsettled question in astrophysical and laboratory plasmas. Here, we report the first observational evidence that magnetic reconnection drives subion-scale turbulence in magnetospheric plasmas by transferring energy to small scales. We employ a spatial "coarse-grained" model of Hall magnetohydrodynamics, enabling us to measure the nonlinear energy transfer rate across scale ℓ at position x. Its application to Magnetospheric Multiscale mission data shows that magnetic reconnection drives intense energy transfer to subion-scales. This observational evidence is remarkably supported by the results from Hybrid Vlasov-Maxwell simulations of turbulence to which the coarse-grained model is also applied. These results can potentially answer some open questions on plasma turbulence in planetary environments.

Ce/Mn/Cr: Y3Al5O12 phosphor ceramics for white LED and LD lighting with a high color rendering index

Ce/Mn/Cr: Y3Al5O12 transparent ceramics with a pure garnet structure and a high color rendering index were prepared by a solid-state reaction method. Mn2+ and Cr3+ enhance the emission between 500 and 700 nm and expand the conventional Ce: YAG phosphors spectrum. The Ce3+ can work both, as activators and sensitizers, and the intense energy transfer from Ce3+ to Mn2+/Cr3+ is realized through the non-radiative and radiative processes. In the sample with the optimized doping concentration the high color rendering index (CRI) value of 75.3 can be achieved under a 450 nm laser diode excitation. The chromaticity coordinates can be tuned from (0.3125, 0.3232) to (0.2917,0.2851) by varying the doping concentration. With the increasing Mn2+/Cr3+ doping concentration, the lifetime of Ce3+, quantum efficiency and luminous efficiency are all gradually decreased. This work effectively offers a scheme for realizing the high color rendering performance of phosphor-converted transparent ceramics in white LEDs/LDs.

Investigation of the Information Possibilities of the Parameters of Vibroacoustic Signals Accompanying the Processing of Materials by Concentrated Energy Flows

Creating systems for monitoring technology processes based on concentrated energy flows is an urgent and challenging task for automated production. Similar processes accompany such processing technologies: intensive thermal energy transfer to the substance, heating, development of the melting and evaporation or sublimation, ionization, and expansion of the released substance. It is accompanied by structural and phase rearrangements, local changes in volumes, chemical reactions that cause perturbations of the elastic medium, and the propagation of longitudinal and transverse waves in a wide frequency range. Vibrational energy propagates through the machine's elastic system, making it possible to register vibrations on surfaces remotely. Vibration parameters can be used in monitoring systems to prevent negative phenomena during processing and to be a tool for understanding the processes' kinetics. In some cases, it is the only source of information about the progress in the processing zone.

Energy Transfer and Electron Heating in Turbulent Flux Pileup Region

AbstractWe report observations of intense energy transfer developed within a flux pileup region (FPR) inside a plasma jet in the Earth's midtail. Strong electromagnetic turbulences, with ( and are wave numbers perpendicular and parallel to background magnetic field respectively), are observed together with intermittent sub‐ion‐scale structures, generating intense fluctuating electric fields and currents inside the FPR. The highly anisotropic turbulence is carried by kinetic Alfvénic waves with ( is ion gyroradius), which are weakly damped due to electron Landau resonance and cause electron heating with a ratio close to 4 eV/s. Concurrent with the ion‐scale turbulences and structures, strong energy conversion occurs inside the FPR (stronger than that at the jet front), with magnetic field energy being dissipated into particle energy, leading to efficient electron acceleration. These results highlight the crucial role played by turbulent FPRs in energy transfer in the magnetosphere.

High-Performance Ternary Organic Solar Cells Enabled by Introducing a New A-DA'D-A Guest Acceptor with Higher-Lying LUMO Level.

A ternary strategy is viable to minimize the trade-off between short-circuit current density (Jsc) and open-circuit voltage (Voc) in organic solar cells. Generally, the ternary OSCs can achieve a higher PCE than the binary counterparts by subtly utilizing the particular photoelectric properties of the third material. In this regard, we choose BTP-CC with a higher-lying LUMO level based on a fused TPBT (dithienothiophen[3.2-b]-pyrrolobenzothiadiazole) central framework and CC (2-(6-oxo-5,6-dihydro-4H-cyclopenta [b]thiophen-4-ylidene) malononitrile) flanking groups as the third component to broaden the light-absorption spectrum, regulate the bulk heterojunction (BHJ) morphology, improve the Voc, and reduce the charge recombination in OSCs. In addition, BTP-CC demonstrates intense intermolecular energy transfer to Y6 by fluorescence resonance energy transfer (FRET) pathway, which is due to the photoluminescence (PL) spectrum of BTP-CC covering the absorption region of Y6. The PM6:Y6:BTP-CC based ternary OSC achieves a champion PCE of 17.55%. Further investigation indicates that introduction of BTP-CC could reduce the trap states in OSCs, leading to an increased charge carrier density. Moreover, the incorporation of BTP-CC could improve the device stability. These results demonstrated that BTP-CC is important in improving the photovoltaic performance of ternary OSCs, and this work also provides a guideline for constructing ideal ternary OSCs in the future.

High-power 2.8 μm lasing in a lightly-doped Er:CaF2 crystal

Er3+-doped crystals pumped by laser diode (LD) is an effective way to obtain near 3 μm laser, which has advantages of low cost and compact structure. CaF2 and SrF2 crystals have the fluorite structure makes Er3+ ions easy to form “clusters”, this effect shortens the space between Er3+ ions, then bring intense interionic energy transfer inside the lightly-doped crystal. Due to the existence of “clusters”, not only the self-termination process was solved, but also the severe thermal damage during the Er3+ 2.8 μm laser generation was avoided. In this work, high quality 1.7 at.% Er:CaF2 laser crystals have been successfully grown by temperature gradient method. LD pumped 2756.6 nm laser with maximum output power of 2.32 W was achieved. It is the highest laser output power generated by LD-pumped Er3+-doped fluoride crystals in recent years. Furthermore, we also demonstrated the 1532 nm LD pumped 1.7 at.% Er:CaF2 laser performance, which proved the strongly energy transfer inside the lightly-doped Er:CaF2 crystal. These results are valuable to the development of the mid-infrared laser towards the direction of compact structure and low cost.

Energy transfer of hypersonic and high-enthalpy boundary layer instabilities and transition

Flow instability of hypersonic and high-enthalpy boundary layers with thermal-chemical nonequilibrium (TCNE) effects is studied for Mach numbers of up to 15. It is quantitatively illustrated that the TCNE effects change the disturbance characteristics predominantly through mean flow modification. In the oblique-mode breakdown case, the intensive energy transfer between the selected modes and their harmonic waves is found to occur where they interact strongly with the mean flow. (L${}_{\mathrm{\ensuremath{\Gamma}}}$ and N${}_{\mathrm{\ensuremath{\Gamma}}}$ in the figure are separately the energy transfer through the linear and nonlinear terms in the disturbance energy-norm equation.)

Overview of Innovative Technologies in Liquid‐Liquid Extraction Regarding Flexibility

AbstractAs a result of increasing market volatility and product diversification the technology requirements will change in the future. Flexibility needs to be increased, enabling a large operating window while maintaining intensive mass and energy transfer and resource‐efficiency. A promising approach is using innovative small‐scale technologies. To assess flexibility, the technologies must be characterized in a wide range of operating parameters and physical properties. Therefore, research work on innovative technologies for liquid‐liquid extraction is presented.

Luminescence behavior of Eu3+ in silica glass containing GdVO4: Eu nanocrystals

Transparent nanocrystalline glass (NCG) with GdVO4:Eu nanocrystals embedded in sintered nanoporous silica glass (NPSG) is synthesized, and intense photoluminescence and energy transfer are observed. X-ray diffraction (XRD), micro-Raman spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM) analyses confirm that GdVO4:Eu nanocrystals are dispersed in silica glass. The photoluminescence intensity of Eu3+ is significantly enhanced by the microcrystallization process. After microcrystallization, the photoluminescence intensity increases by 41 and 14 times for glass that has Eu3+ singly doped and glass codoped with Gd3+, VO43−, and Eu3+, respectively. When Gd3+ and Eu3+, Gd3+ and V5+, and V5+ and Eu3+ are respectively double-doped, the efficiencies of Gd3+ → Eu3+, VO43- → Eu3+, and Gd3+ → VO43− energy transfers are assayed to be 22.3%, 24.7%, and 70.1%, respectively. In Eu3+, Gd3+, and V5+ triple-doped samples, in addition to the above energy transfer processes, there is a Gd3+ → VO43- → Eu3+ energy transfer. Nevertheless, VO43- → Eu3+ is still the main process. Especially after microcrystallization, the transfer efficiency of VO43- → Eu3+ is significantly increased to 90.9% because the lattice site of Gd3+ is replaced by Eu3+ in GdVO4 crystallites.

Role of H3BO3 and Sr2+/K+ in the luminescent property of NaBaB9O15:Eu2+

A series of Na1-zKzBa1-ySryB9O15:Eu2+ were synthesized by the high temperature solid state method. H3BO3 excess makes it easier for Eu2+ to enter Na+ site, and the single-phase "blue + green" double emission band can be observed, which is proved by thermoluminescence and the change of crystal structure. Moreover, there exists an intense energy transfer from the blue-emitting center to the green-emitting center, which is proved by the decay curve. The occupation of Eu2+ can be tuned by the introduction of Sr2+ and K+ in NaBaB9O15. Further, the highly thermal-sensitive property of NaBaB9O15: 1%Eu2+ makes it feasible for its potential application in luminescent ratiometric thermometers with wide temperature range. In addition, the disorder degree of matrix cations increases with the incorporation of K+, which improves the thermal stability.

Time-Periodic Inertial Range Dynamics.

A wide class of physical systems exhibit scale invariance. While the statistical properties of such behavior can often be investigated by theoretical and experimental means, its dynamics are notoriously hard to parse. We investigate scale-invariant dynamics through an unstable periodic orbit. This orbit coexists with turbulence of an incompressible fluid and yields a significant Kolmogorov energy spectrum. We identify events of intense energy transfer across spatial scales and relate them to vortical dynamics. The results support a recently proposed mechanism for turbulent energy transfer.

Regimes of two-dimensional energy channeling in the inertially coupled unit-cell model subjected to an asymmetric potential

We analyze the stationary and non-stationary states emerging in a two-dimensional (2D) model consisting of an outer element that incorporates an internal rotator and is subjected to a 2D anharmonic and non-symmetric local potential. We focus on the effect of the asymmetry of the potential on the mechanism of formation and bifurcations of various stationary and non-stationary regimes in the system. The non-stationary regimes are characterized by an intense bi-directional energy transfer between the axial and lateral vibrations of the main element as well as the regimes of unidirectional energy locking. We show that the transitions between the different states of the system are controlled by the motion of the internal rotator. Our analysis is based on the complexification-averaging procedure and the singular multiscale asymptotic method. Investigation of the system's dynamics in the vicinity of the 1:1:1 resonance enables us to reproduce the bifurcation structure of the stationary regimes and describe the formation mechanisms of highly non-stationary states of intense energy transfer. Our analysis shows that the most important effect of the asymmetric potential is the breakdown of a unique complete bi-directional energy channeling mechanism into two separate mechanisms that correspond to incomplete horizontal-to-vertical and vertical-to-horizontal energy transfer, respectively, and are enabled at two different critical values of the main bifurcation parameter. Results of the analysis are in good agreement with the numerical simulations of the full model.

Small-scale structure and energy transfer in homogeneous turbulence

We use high-resolution velocity measurements in a jet-stirred zero-mean-flow facility to investigate the topology and energy transfer properties of homogeneous turbulence over the Reynolds number range$Re_{\unicode[STIX]{x1D706}}\approx 300$–500. The probability distributions of the enstrophy and strain-rate fields show long tails associated with the most intense events, while the weaker events behave as random variables. The high-enstrophy and high-strain structures are shaped as tube-like and sheet-like objects, respectively, the latter often wrapped around the former. Both types of structures have thickness that scales in Kolmogorov units, and display self-similar topology over a wide range of scales. The small-scale turbulence activity is found to be strongly correlated with the large-scale activity, suggesting that the phenomenon of amplitude modulation (previously observed in advection-dominated shear flows) is not limited to specific production mechanisms. Observing the significant variations in spatially averaged enstrophy, we heuristically define hyperactive and sleeping states of the flow: these also correspond to, respectively, high and low levels of large-scale velocity gradients. Moreover, the hyperactive and sleeping states contribute very differently to the inter-scale energy flux, characterized via the nonlinear transfer term in the Kármán–Howarth–Monin equation. While the energy cascades to smaller scales along the jet-axis direction, a weaker but sizable inverse transfer is observed along the transverse direction; a behaviour so far only observed in spatially developing flows. The hyperactive states are characterized by very intense energy transfers, while the sleeping states account for weaker fluxes, largely directed from small to large scales. This implies that the form of energy cascade depends on the presence (or absence) of intense turbulent structures. These results are at odds with the classic concept of the energy cascade between adjacent scales, but are compatible with the view of a cascade in physical space.

Emergence of non-stationary regimes in one- and two-dimensional models with internal rotators

In the present paper, we give a selective review of some very recent works concerning the non-stationary regimes emerging in various one- and two-dimensional models incorporating internal rotators. In one-dimensional models, these regimes are characterized by the intense energy transfer from the outer element, subjected to initial or harmonic excitation, to the internal rotator. As for the two-dimensional models (incorporating internal rotators), we will mainly focus on the two special dynamical states, namely a state of the near-complete energy transfer from longitudinal to lateral vibrations of the outer element as well as the state of a permanent, unidirectional energy locking with mild, spatial energy exchanges. In this review, we will discuss the recent theoretical and experimental advancements in the study of essentially nonlinear mechanisms governing the formation and bifurcations of the regimes of intense energy transfer. The present review is composed of two parts. The first part will be mainly devoted to the emergence of resonant energy transfer states in one-dimensional models incorporating internal rotators, while the second part will be mainly concerned with the manifestation of various energy transfer states in two-dimensional ones.This article is part of the theme issue 'Nonlinear energy transfer in dynamical and acoustical systems'.

Passive nonlinear targeted energy transfer.

Nonlinearity in dynamics and acoustics may be viewed as scattering of energy across frequencies/wavenumbers. This is in contrast with linear systems when no such scattering exists. Motivated by irreversible large-to-small-scale energy transfers in turbulent flows, passive targeted energy transfers (TET) in mechanical and structural systems incorporating intentional strong nonlinearities are considered. Transient or permanent resonance captures are basic mechanisms for inducing TET in such systems, as well as nonlinear energy scattering across scales caused by strongly nonlinear resonance interactions. Certain theoretical concepts are reviewed, and some TET applications are discussed. Specifically, it is shown that the addition of strongly nonlinear local attachments in an otherwise linear dynamical system may induce energy scattering across scales and 'redistribution' of input energy from large to small scales in the linear modal space, in similarity to energy cascades that occur in turbulent flows. Such effects may be intentionally induced in the design stage and may lead to improved performance, e.g. it terms of vibration and shock isolation or energy harvesting. In addition, a simple mechanical analogue in the form of a nonlinear planar chain of particles composed of linear stiffness elements but exhibiting strong nonlinearity due to kinematic and geometric effects is discussed, exhibiting similar energy scattering across scales in its acoustics. These results demonstrate the efficacy of intentional utilization of strong nonlinearity in design to induce predictable and controlled intense multi-scale energy transfers in the dynamics and acoustics of a broad class of systems and structures, thus achieving performance objectives that would be not possible in classical linear settings.This article is part of the theme issue 'Nonlinear energy transfer in dynamical and acoustical systems'.

High‐Efficiency Ternary Polymer Solar Cells Based on Intense FRET Energy Transfer Process

A new wide band gap polymer PBDTPS‐FTAZ is designed and synthesized to form complementary absorption with non‐fullerene acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)dithieno[2,3‐d':2,3'‐d']‐s‐indaceno[1,2‐b:5,6‐b'] dithiophene (ITIC). The optimized device utilizing PBDTPS‐FTAZ:ITIC as active layer exhibits a power conversion efficiency (PCE) of 8.53%. The external quantum efficiency (EQE) spectrum indicates that the binary‐blend device suffers relatively low photo response in the 450–550 nm region. Therefore, the fullerene derivative PC71BM and a wide band gap donor polymer P(p‐FDBND‐2T) with the absorption region of 450–550 nm are added to the PBDTPS‐FTAZ:ITIC system to construct ternary blend solar cell, respectively. As a result, ternary‐blend solar cells based on two configurations (D:A1:A2 and D1:D2:A) both deliver high PCE over 10% using the conventional device structure. Interestingly, the D1:D2:A type ternary solar cell exhibits a higher open circuit voltage (VOC) along with an intense energy transfer process regardless of the undesirable energy level alignment and reached a high PCE of 11.46%.