Dominant channels of exciton spin relaxation in photoexcited self-assembled (In,Ga)As quantum dots

We present a comprehensive theoretical investigation of spin relaxation processes of excitons in photoexcited self-assembled quantum dots. The exciton spin relaxations are considered between dark- and bright-exciton states via the channels created by various spin-admixture mechanisms, including electron Rashba and Dresselhaus spin- orbital couplings (SOCs), hole linear and hole cubic SOCs, and electron hyperfine interactions, incorporated with single- and double-phonon processes. The hole-Dresselhaus SOC is identified as the dominant spin-admixture mechanism, leading to relaxation rates as fast as ∼10−2 ns−1, consistent with recent observations. Moreover, due to significant electron-hole exchange interactions, single-phonon processes are unusually dominant over two-phonon ones in a photoexcited dot even at temperatures as high as 15 K

Numerical Investigation on Flow and Heat Transfer Performance of Supercritical Carbon Dioxide Based on Variable Turbulent Prandtlnumber Model

Flow and heat transfer characteristic of supercritical carbon dioxide (SCO2) are numerically investigated in the horizontal and vertical tubes. TWL turbulent Prandtl number model could well describe the behavior of SCO2 affected by the buoyancy. Under the cooling condition, the heat transfer performance of SCO2 along the upward direction is best and that along the downward direction is worst when bulk fluid temperatures are below the pseudocritical temperature. Reducing the ratio of heat flux to mass flux could decrease the difference of convective heat transfer coefficient in three flow directions. Under the heating condition, heat transfer deterioration only occurs in vertical upward and horizontal flow directions. Heat transfer deterioration of SCO2 could be delayed by increasing the mass flux and the deterioration degree is weakened in the second half of tube along the vertical upward flow direction. Compared with the straight tube, the corrugated tube shows better comprehensive thermal performance

BronchoTrack: Airway Lumen Tracking for Branch-Level Bronchoscopic Localization

Localizing the bronchoscope in real time is essential for ensuring intervention quality. However, most existing methods struggle to balance between speed and generalization. To address these challenges, we present BronchoTrack, an innovative real-time framework for accurate branch-level localization, encompassing lumen detection, tracking, and airway association.To achieve real-time performance, we employ a benchmark lightweight detector for efficient lumen detection. We are the first to introduce multi-object tracking to bronchoscopic localization, mitigating temporal confusion in lumen identification caused by rapid bronchoscope movement and complex airway structures. To ensure generalization across patient cases, we propose a training-free detection-airway association method based on a semantic airway graph that encodes the hierarchy of bronchial tree structures.Experiments on nine patient datasets demonstrate BronchoTrack's localization accuracy of 85.64 \%, while accessing up to the 4th generation of airways.Furthermore, we tested BronchoTrack in an in-vivo animal study using a porcine model, where it successfully localized the bronchoscope into the 8th generation airway.Experimental evaluation underscores BronchoTrack's real-time performance in both satisfying accuracy and generalization, demonstrating its potential for clinical applications

Numerical investigation on the thermal-hydraulic performance of supercritical CO₂ in a modified airfoil fins heat exchanger

The numerical studies on the modified airfoil fins channel using supercritical CO2 as working fluid showed that front-dense and rear-sparse (FDRS) and front-sparse and rear-dense (FSRD) distributions of fins could enhance heat transfer by improving the distribution uniformity of temperature difference in channel. The match of local dense distribution of fins with the region near pseudocritical point could obtain better overall thermal performance in the modified airfoil fins heat exchanger. The differences of thermal-hydraulic performance among channels with uniform, FDRS and FSRD distributions of fins could be explained with field synergy principle. The FSRD distribution of fins is the optimum scheme in the three distributions of the modified airfoil fins channel, because its comprehensive performance is 23–29 % higher than that of the uniform distribution of fins and 2–7.6 % higher than that of the FDRS distribution of fins. The present work provides insights into the mechanisms of supercritical CO2 heat transfer characteristics as well as practical guidance on the design and optimisation of relevant components