Reverse Intersystem Crossing Managing Assistant Dopant for High External Quantum Efficiency Red Organic Light-Emitting Diode

Thermally activated delayed fluorescence (TADF) materials working as an assistant dopant with reduced Dexter energy transfer rate was designed by replacing the donor moiety of 2,3,5,6-tetra(9H-carbazol-9-yl) terephthalonitrile (4CzTPN) with 5H-benzo[4,5]thieno[3,2-c]carbazole...

Properties of Hall-MHD Turbulence at Sub-Ion Scales: Spectral Transfer Analysis

We present results of a multiscale study of Hall-magnetohydrodynamic (MHD) turbulence, carried out on a dataset of compressible nonlinear 2D Hall-MHD numerical simulations of decaying Alfvénic turbulence. For the first time, we identify two distinct regimes of fully developed turbulence. In the first one, the power spectrum of the turbulent magnetic fluctuations at sub-ion scales exhibits a power law with a slope of ∼−2.9, typically observed both in solar wind and in magnetosheath turbulence. The second regime, instead, shows a slope of −7/3, in agreement with classical theoretical models of Hall-MHD turbulence. A spectral-transfer analysis reveals that the latter regime occurs when the energy transfer rate at sub-ion scales is dominated by the Hall term, whereas in the former regime, the governing process is the dissipation (and the system exhibits large intermittency). Results of this work are relevant to the space plasma community, as they may potentially reconcile predictions from theoretical models with results from numerical simulations and spacecraft observations.

Impact of Switchbacks on Turbulent Cascade and Energy Transfer Rate in the Inner Heliosphere

Recent Parker Solar Probe (PSP) observations of inner heliospheric plasma have shown an abundant presence of Alfvénic polarity reversal of the magnetic field, known as “switchbacks.” While their origin is still debated, their role in driving the solar wind turbulence has been suggested through analysis of the spectral properties of magnetic fluctuations. Here, we provide a complementary assessment of their role in the turbulent cascade. The validation of the third-order linear scaling of velocity and magnetic fluctuations in intervals characterized by a high occurrence of switchbacks suggests that, irrespective of their local or remote origin, these structures are actively embedded in the turbulent cascade, at least at the radial distances sampled by PSP during its first perihelion. The stronger positive energy transfer rate observed in periods with a predominance of switchbacks indicates that they act as a mechanism injecting additional energy in the turbulence cascade.

Research on the design and application of capillary heat exchangers for heat pumps in coastal areas

This study investigated the optimal design of a capillary heat exchanger device for the heat pump system and its innovative engineering application in a building. The overall aim was to use a capillary heat exchanger to obtain energy in coastal areas for promoting renewable energy in low-carbon building design. Initially, the main factors affecting the efficiency of the capillary heat exchanger were identified, a mathematical model was then established to analyse the heat transfer process. The analysis showed the flow rate and the capillary length are the key factors affecting the efficiency of the capillary heat exchanger. Secondly, to optimize the structural design of the capillary heat exchanger, the heat energy transfer is calculated with different lengths of the capillary under various flow rates in summer and winter conditions, respectively. Thirdly, a typical building is selected to analyse the application of the capillary heat exchanger for extracting energy in the coastal area. The results show the performance of the selected capillary heat exchanger heat pump system, in winter, the heat energy transfer rate is 60 W/m2 when the seawater temperature is 3.7 °C; in summer, the heat energy transfer rate is 150 W/m2 when the seawater temperature is 24.6 °C. Finally, the above field test results were examined using a numerical simulation model, the test and simulation results agree with each other quite well. This paper is conducive in promoting the development of the capillary heat exchanger heat pump as an innovative sustainable technology for net-zero energy and low carbon buildings using renewable energy in coastal areas. Practical application: A recently proposed capillary heat exchanger is used as an energy extraction and utilisation device to obtain energy in coastal areas for promoting renewable energy in low-carbon building design. This paper explores the application of a capillary heat exchanger as both cold and heat sources for application in typical low-rise buildings. The analysis of the heat energy transfer rate of a typical low-rise building located in a coastal area in summer and winter provides guidance for the application of capillary heat exchangers.

Inverse energy cascade in ocean macroscopic turbulence: Energy transfer rate ε and Richardson-Obhukov constant g from an surface drifter experiment in the Benguela upwelling system

<p>We derive the energy transfer rate ε from the 3<sup>rd</sup> order relative (longitudinal)  velocity structure function <Δu<sub>l</sub><sup>3</sup>>=(3/2)εs from ocean surface drifter trajectories in the turbulent mixed layer of the Benguela upwelling region off the coast of Namibia.  Combination with the  mean squared pair separation<s<sup>2</sup>(t)> =gεt<sup>3 </sup>reveals the Richardson-Obhukov constant g≅0.5, which is remarkably close to the one measured in  controlled two-dimensional turbulent flows in laboratory. We verify the  two coupled  cascades of energy (upscale/inverse) and enstrophy (downwscale) by  the  theoretically predicted  slope 1  for <Δu<sub>l</sub><sup>3</sup>> for inertial scales (above the injection scale) and slope 2 for  the 2<sup>nd</sup> order structure function <Δu<sub>l</sub><sup>2</sup>> for non-local scales (below the injection scale) respectively. We detect  additional 'ballistic contributions' in the central regime of the corresponding probability distribution P(st) of relative separations s for fixed time t, leading to an additional  power law factor s<sup>-α</sup> with  α ≅ 5/3. The algebraic decay with 1<α <2 revives  to the relevance of Levy distributions in the stochastic description of the turbulent transport process in contrast to former claims. Our findings  of a positively skewed   probability distribution P(Δu<sub>l</sub>s) of relative longitudinal velocity Δu<sub>l</sub>  for inertial scales s renews the question of intermittency in the  inverse energy cascade.</p>

Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution and Effective Excitation

<p>Differential flow among different ion species are always observed in the solar wind, and such ion differential flow can provide a free energy to drive the Alfven/ion-cyclotron and fast-magnetosonic/whistler instabilities. Previous works on the ion beam instability are mainly focused on the solar wind parameters at 1 au. We extend this study using the radial model of the magnetic field and plasma parameters in the inner heliosphere. We present the distributions of the energy transfer rate among the unstable waves and the particles, which would be useful to predict the change of parallel and perpendicular temperatures during the instability evolution. Moreover, we propose an effective growth length to estimate the effective growth in each instability, and we explore that the oblique Alfven/ion-cyclotron instability, the oblique fast-magnetosonic/whistler instability and the oblique Alfven/ion-beam instability can be effectively driven by proton beams having speed of 500-2000 km/s in the solar atmosphere. We also show that the unstable waves driven by the proton beam instability would be responsible for the solar corona heating. These predictions can be checked by in situ satellite measurements in the inner heliosphere.</p>

Comparing turbulence in a Kelvin-Helmholtz instability region across the terrestrial magnetopause

The properties of turbulence observed within the plasma originating from the magnetosheath and the magnetospheric boundary layer, which have been entrained within vortices driven by the Kelvin-Helmholtz Instability (KHI), are compared. The goal of such a study is to determine similarities and differences between the two different regions. In particular, we study spectra, intermittency and the third-order moment scaling, as well as the distribution of a local energy transfer rate proxy. The analysis is performed using the Magnetospheric Multiscale (MMS) data from a single satellite that crosses longitudinally the KHI. Two sets of regions, one set containing predominantly magnetosheath plasma and the other containing predominantly magnetospheric plasma, are analyzed separately, thus allowing us to explore turbulence properties in two portions of very different plasma samples. Results show that the turbulence in the two regions is different, with the boundary layer plasma including current structures that may not be originated by the turbulent cascade. This suggests that the observed turbulence is affected by the KHI.

Numerical Investigation of Nanoparticles Shape Impacts on Thermal Energy Transfer and Flow Features of Nanofluid Impingement Jets

Today, energy transfer enhancement techniques have received much attention for design and manufacturing more efficient systems in various industries such as automotive, computers, electronics, and so forth. One way to achieve high-efficiency cooling systems is to use impingement jet cooling. In the present study, a numerical study has been conducted on nanofluid impingement jet in the vertical position to investigate the fluid flow characteristics and thermal energy transfer features. The working fluid in this study is a nanofluid with water–ethylene glycol mixture as base fluid and nanoparticles of boehmite alumina. The flow is considered to be laminar, steady-state, two-dimensional, symmetrically axial, for which the finite volume method is used to solve the equations. The effect of the Reynolds number variations, the volume fraction of nanoparticle, and different nanoparticle shapes (including spherical, plate, blade, cylindrical, and brick shapes) on thermophysical features of the flow are studied. The results reveal that the increasing Reynolds number and the increasing volume fraction of nanoparticles improves the thermal energy transfer rate. The highest Nusselt number leads to a maximum of energy transfer related to nanofluids with platelet and cylindrical nanoparticles, while the lowest thermal energy transfer rate is related to nanofluids containing spherical nanoparticles. Moreover, it is illustrated that nanofluids with platelets nanoparticles, because of their higher effective viscosity compares to other nanofluids, experience the highest pressure drop and those of with spherical nanoparticles show the lowest pressure drop.