Abstract With the aid of a electro-opto-thermal model of a two-dimensional (2-D) verticalcavity surface-emitting laser (VCSEL) array, the thermal characteristics of a 4×4 VCSEL array is simulated. It is shown that there is a higher temperature in the central region of the device, which limits the optical output performance. In order to enhance the optical output power, a novel VCSEL array with non-uniform oxidation aperture is designed. As a result, the peak junction temperature is decreased, and the non-uniformity of junction temperature and bias current density among array cells are improved obviously. Furthermore, experimental results demonstrate that the optical output power of the novel VCSEL array is increased from 33.5mW to 38.6mW with an improvement of 15.22% and a superior far-field light spot, when compared with the uniform device. The non-uniform oxidation aperture design sheds light on a effective method to enhances the thermal behaviour and optical performance of VCSEL arrays.
The proximity effect in multilayer structures with dirty two band superconductors and ferromagnets is investigated here. With a homogeneous exchange field and interband scattering in the ferromagnetic layer, the condensate functions that penetrate the ferromagnet are coupled up. This coupling effect is intensively suppressed by the exchange field and modulated by the diffusion coefficients of the two bands. Such coupling also affects the superconductor where the condensate functions of the two bands are also coupled up through the proximity effect. An inhomogeneous exchange field raises the damped oscillation of the condensate functions as the spatial distance from the interface increases. There is a 0−π phase shift when the ferromagnetic layer thickness varies beyond the ferromagnetic coherence length.
An organic deep ultraviolet (DUV) photodetector (PD) with a response peak at 270 nm was fabricated. NPB and BAlq were employed as electron donor and acceptor, respectively, and polymer PEDOT:PSS was used as the transparent anode. The peak response of 0.14 A/W under illumination of 270-nm light with an intensity of 1.35 mW/cm 2 and a detectivity of 8.26×10 11 cmHz 1/2 W -1 at -12 V were achieved, and the corresponding quantum efficiency η reaches 64.3%. The PDs exhibit a low dark current of 8.97×10 -8 A/cm 2 , and the photo-to-dark current ratio is about 2.1×10 3 at -12 V. The realization of DUV detection is attributed to the strong absorption of shorter UV wavelengths of acceptor BAlq and high transmittance of PEDOT:PSS anode in DUV region. The mechanism of harvesting high performance is also discussed in detail.
Micropillar cavities containing 1.55 μm quantum dots are required for silica-fiber based quantum information processing. The straight way is to construct micropillars consisting of InGaAsP/InP distributed Bragg reflectors. We perform a systematic study mainly on optical properties correlated to the micropillar diameter. As expected, the mode wavelength increases with extending micropillar diameter and tends to saturate at 1.55 μm for the diameter larger than 2.0 μm. Able to be as high as 104, the quality factor, however, is almost independent of pillar diameter, which may be the result of the small refractive index contrast. The Purcell factor reaches highest ( >130) at pillar diameter of ∼0.6 μm, suggesting that these cavities could serve as efficient 1.55 μm single photon sources. The output efficiency increases with extending diameter, and is acceptably good at small diameters. Although not easy in fabrication technique, this cavity provides monolithic scheme for constructing 1.55 μm single photon sources.
Ultrathin MgB2 superconducting films with a thickness down to 7.5 nm are epitaxially grown on (0001) Al2O3 substrate by hybrid physical-chemical vapor deposition method. The films are phase-pure, oxidation-free and continuous. The 7.5 nm thin film shows a Tc(0) of 34 K, which is so far the highest Tc(0) reported in MgB2 with the same thickness. The critical current density of ultrathin MgB2 films below 10 nm is demonstrated for the first time as Jc ~ 10^6 A cm^{-2} for the above 7.5 nm sample at 16 K. Our results reveal the excellent superconducting properties of ultrathin MgB2 films with thicknesses between 7.5 and 40 nm on Al2O3 substrate.
The goal of this study was to investigate whether the combined PET/CT radiomic features of the primary tumor and lymph node could predict lymph node metastasis (LNM) of resectable non-small cell lung cancer (NSCLC) in stage T2-4.This retrospective study included 192 NSCLC patients who underwent tumor and node dissection between August 2016 and December 2017 and underwent 18F-fluorodeoxyglucose (18F-FDG) PET/CT scanning 1-3 weeks before surgery. In total, 192 primary tumors (> 3 cm) and 462 lymph nodes (LN > 0.5 cm) were analyzed. The pretreatment clinical features of these patients were recorded, and the radiomic features of their primary tumor and lymph node were extracted from PET/CT imaging. The Spearman's relevance combined with the least absolute shrinkage and selection operator was used for radiomic feature selection. Five independent machine learning models (multi-layer perceptron, extreme Gradient Boosting, light gradient boosting machine, gradient boosting decision tree, and support vector machine) were tested as classifiers for model development. We developed the following three models to predict LNM: tumor PET/CT-clinical (TPC), lymph PET/CT-clinical (LPC), and tumor and lymph PET/CT-clinical (TLPC). The performance of the models and the clinical node (cN) staging was evaluated using the ROC curve and confusion matrix analysis.The ROC analysis showed that among the three models, the TLPC model had better predictive clinical utility and efficiency in predicting LNM of NSCLC (AUC = 0.93, accuracy = 85%; sensitivity = 0.93; specificity = 0.75) than both the TPC model (AUC = 0.54, accuracy = 50%; specificity = 0.38; sensitivity = 0.59) and the LPC model (AUC = 0.82, accuracy = 70%; specificity = 0.41; sensitivity = 0.92). The TLPC model also exhibited great potential in predicting the N2 stage in NSCLC (AUC = 0.94, accuracy = 79%; specificity = 0.64; sensitivity = 0.91).The combination of CT and PET radiomic features of the primary tumor and lymph node showed great potential for predicting LNM of resectable T2-4 NSCLC. The TLPC model can non-invasively predict lymph node metastasis in NSCLC, which may be helpful for clinicians to develop more rational therapeutic strategies.
A constant volume bomb was used to study diesel combustion characteristics under air and airethanol atmospheres and ambient pressure of 3 MPa.The ignition delay and lift-off length of diesel flame were observed at varied initial temperatures under the two atmospheres.Using zero-dimensional simulation model and the detail reaction mechanism of n-heptane combining ethanol,the ignition process of n-heptane and n-heptane mixing with ethanol was studied.The results show that,ethanol addition increases the ignition delay and lift-off length of diesel flame.For stabilized flame,the lift-off length of flame at the ethanol atmosphere varies greatly compared with that at the pure air atmosphere.Within the temperature range of 800-900 K,the ignition delay and lift-off length of diesel flame decrease with the increase of temperature,and they are more sensitive to the temperature at the ethanol atmosphere.Simulation results shows that,low temperature reaction delay is increased by ethanol addition as the concentration of OH is low,and low temperature reaction is suppressed,however,heat release duration of high temperature reaction is decreased,and high temperature reaction is promoted.
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