Improved ground-state modulation characteristics in 1.3 μm InAs/GaAs quantum dot lasers by rapid thermal annealing

We investigated the ground-state (GS) modulation characteristics of 1.3 μm InAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. The choice of annealing conditions was determined from our recently reported results. With reference to the as-grown QD lasers, one obtains approximately 18% improvement in the modulation bandwidth from the annealed QD lasers. In addition, the modulation efficiency of the annealed QD lasers improves by approximately 45% as compared to the as-grown ones. The observed improvements are due to (1) the removal of defects which act as nonradiative recombination centers in the QD structure and (2) the reduction in the Auger-related recombination processes upon annealing

Small signal modulation characteristics of quantum dot lasers and the effect of annealing and doping

The demand for bandwidth capacity is increasing exponentially due to the spread of high-speed internet services. A significant increase in capacity is achieved in fibre optical access networks. Semiconductor lasers operating at wavelengths around 1.3 μm, where the standard single mode fibre has minimum dispersion, are key components in such networks. Thus, they have attracted much research interest in recent years. The discovery of self-organized epitaxial quantum dots (QDs) resulted in multiple breakthroughs in the field of the physics of zero-dimensional (0-D) heterostructures and allowed the advancement of optoelectronic devices. The most remarkable advancement involved lasers. The most advanced results obtained for lasers are based on the InGaAs/GaAs QDs by the Stranski-Krastanow growth. InAs is currently the most optimized candidate material for constructing low-cost and high-performance QD lasers on GaAs substrates because of its low threshold current density and its temperature insensitivity compared to lasers made from the conventional InGaAs/InP material system. Superior static performances have been demonstrated for 1.3 μm InAs/GaAs QD lasers. However, InAs/GaAs QD lasers have not fulfilled the initial expectation of demonstrating superior dynamic characteristics over Quantum Well (QW) lasers. The aim of this research study is to characterize the performances of InAs/InGaAs QD lasers and to suggest a method to improve these performances through p-doping and post-growth rapid thermal annealing. A systematic study has been performed on undoped and p-doped ten-layer InAs/InGaAs QD lasers to investigate the characteristic parameters related to lasing behaviour. The high-speed performance of these lasers will be targeted. During this study, high-speed characterizations were carried out on undoped ten-layer InAs/InGaAs QD lasers. Their temperature-dependent frequency modulation was investigated from 5 °C to 50 °C. The modulation bandwidth of the intrinsic QD laser was found to be highly temperature sensitive. Although the intrinsic damping-limited modulation bandwidth of the InAs/InGaAs QD laser is as high as 23 GHz, the actual modulation bandwidth is limited by carrier thermalization under continuous-wave operations. A saturation of the resonance frequency was found to be the result of thermal reduction in the differential gain, which may originate from carrier thermalization in intrinsic QDs. In order to improve the performance of the QDs, a series of experiments investigated the effects of p-doping and post-growth rapid thermal annealing (RTA) on the lasing behaviours of the QD lasers. P-doping improved the temperature dependent characteristics of the ten-layer InAs/InGaAs QD lasers. Meanwhile, an improved internal loss and a higher internal differential efficiency were demonstrated in both the undoped and p-doped InAs/InGaAs QD lasers under optimum annealing conditions. By analyzing the modal gain competition of the fabricated QD lasers from the below-ground-state (GS) to the above-excited-state (ES) thresholds, we found that: (i) the onset of ES lasing can be significantly delayed to a higher injection current with optimum annealing conditions, and, (ii) under the same annealing condition, p-doped QD lasers can sustain GS lasing to a higher operating temperature compared to the intrinsic ones. A faster carrier relaxation mechanism was produced in QDs under optimum annealing conditions and this is expected to improve the high-speed modulation characteristics of the QD lasers. QD intermixing has been expected to improve the carrier capture and relaxation and, hence, the high-speed performance of QD lasers. Followed by the successful enhancement of GS lasing in the undoped QD laser with optimum annealing, investigations were carried out to study the effects of intermixing on the high-speed characteristics of the undoped ten-layer InAs/InGaAs QD lasers. Improvements in the temperature stability of the modulation bandwidth were demonstrated in the undoped QD lasers under optimum annealing conditions. The increase in bandwidth at a high temperature from the annealed QD lasers could be due to the reduction in the temperature dependency of the differential gain and the improvement in the internal quantum efficiency. These improvements are attributed to the defects removal, the reduction of the carrier relaxation time in the order of 10-1 ps and the better dots uniformity after optimum RTA. These findings are beneficial for the development of uncooled high-speed QD lasers in fibre optical access networks. Finally, further investigations studied the effects of post-growth RTA on the high-speed characteristics of the p-doped ten-layer InAs/InGaAs QDs where Auger-related recombination processes are more severe. In the p-doped QD lasers, an almost 18% improvement in the modulation bandwidth and an approximately 45% improvement in the modulation efficiency were obtained from the annealed QD lasers compared to the as-grown ones. Through measurements of the total spontaneous emission intensity, the observed improvements in the p-doped QDs are believed to be due to the reduction in the Auger-related recombination processes and the reduction in the defects density in the p-doped QDs upon annealing.Doctor of Philosophy (EEE

High glucose dialysate-induced peritoneal fibrosis: Pathophysiology, underlying mechanisms and potential therapeutic strategies

Peritoneal dialysis is an efficient renal replacement therapy for patients with end-stage kidney disease. However, continuous exposure of the peritoneal membrane to dialysate frequently leads to peritoneal fibrosis, which alters the function of the peritoneal membrane and results in withdrawal from peritoneal dialysis in patients. Among others, high glucose dialysate is considered as a predisposing factor for peritoneal fibrosis in patients on peritoneal dialysis. Glucose-induced inflammation, metabolism disturbance, activation of the renin–angiotensin–aldosterone system, angiogenesis and noninflammation-induced reactive oxygen species are implicated in the pathogenesis of high glucose dialysate-induced peritoneal fibrosis. Specifically, high glucose causes chronic inflammation and recurrent peritonitis, which could cause migration and polarization of inflammatory cells, as well as release of cytokines and fibrosis. High glucose also interferes with lipid metabolism and glycolysis by activating the sterol-regulatory element-binding protein-2/cleavage-activating protein pathway and increasing hypoxia inducible factor-1α expression, leading to angiogenesis and peritoneal fibrosis. Activation of the renin–angiotensin-aldosterone system and Ras-mitogen activated protein kinase signaling pathway is another contributing factor in high glucose dialysate-induced fibrosis. Ultimately, activation of the transforming growth factor-β1/Smad pathway is involved in mesothelial-mesenchymal transition or epithelial-mesenchymal transition, which leads to the development of fibrosis. Although possible intervention strategies for peritoneal dialysate-induced fibrosis by targeting the transforming growth factor-β1/Smad pathway have occasionally been proposed, lack of laboratory evidence renders clinical decision-making difficult. We therefore aim to revisit the upstream pathways of transforming growth factor-beta1/Smad and propose potential therapeutic targets for high glucose-induced peritoneal fibrosis

An updated meta-analysis on the efficacy and safety of hypoxia-inducible factor prolyl hydroxylase inhibitor treatment of anemia in nondialysis-dependent chronic kidney disease

AbstractBackground Renal anemia, a common complication and threat factor of chronic kidney disease (CKD), has long been treated with injectable erythropoietin-stimulating agents (ESAs). As concerns regarding cardiovascular safety and erythropoietin resistance to ESAs have emerged, alternative therapies are urgently needed. Hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI), an oral agent, has been proven to be effective in improving renal anemia. However, the effects of HIF-PHIs on nondialysis-dependent CKD (NDD-CKD) have yet to be supported by updated meta-analyses.Methods A meta-analysis of clinical randomized controlled trials (RCTs) on HIF-PHI treatment of NDD-CKD patients based on PubMed, EMBASE, and Cochrane databases as of July 16th, 2023, was conducted. The primary outcomes were the level of hemoglobin (Hb) postintervention and the ratio of Hb responses. Most of the analysis was conducted via RevMan 5.3 software using a random-effects model. Stata (version 15.0) was used to analyze the publication bias.Results Twenty-two studies with a total of 7178 subjects in the HIF-PHI group, 3501 subjects in the ESA group and 2533 subjects in the placebo group were enrolled. HIF-PHIs increased the level of Hb and improved iron metabolism but were not inferior to ESAs in terms of safety.Conclusions HIF-PHIs may be a convenient and safe alternative to ESAs in patients with NDD-CKD and anemia

Valve Internal Leakage Rate Quantification Based on Factor Analysis and Wavelet-BP Neural Network Using Acoustic Emission

Valve internal leakage is easily found because of various defects resulting from environmental factors and load fluctuation. The timely detection of valve internal leakage is of great significance to the safe operation of pipelines. As an effective means for detecting valve internal leakage, the acoustic emission technique is characterized by nonintrusive and strong anti-interference ability, which can realize the in situ monitoring of the valve running status in real time. In this paper, acoustic emission signals from an internal leaking valve were obtained experimentally. Then, the dimensionality reduction technology based on factor analysis was introduced to the processing of valve internal leakage detection data. Next, the wavelet decomposition was carried out to decompose the sample feature set into four subsets. Finally, the decomposed sample feature sets were inputted into the error backpropagation (BP) neural network quantitative model, respectively. The optimized results show that the predicted internal leakage rate by the wavelet-BP neural network model has good precision with an error of less than 10%. The wavelet-BP neural network model can realize the analysis of the valve internal leakage rate quantitatively and has good robustness, which provides technical support and guarantees the safe operation of natural gas pipeline valves

Recent Progress on Graphene-Based Nanocomposites for Electrochemical Sodium-Ion Storage

In advancing battery technologies, primary attention is paid to developing and optimizing low-cost electrode materials capable of fast reversible ion insertion and extraction with good cycling ability. Sodium-ion batteries stand out due to their inexpensive price and comparable operating principle to lithium-ion batteries. To achieve this target, various graphene-based nanocomposites fabricate strategies have been proposed to help realize the nanostructured electrode for high electrochemical performance sodium-ion batteries. In this review, the graphene-based nanocomposites were introduced according to the following main categories: graphene surface modification and doping, three-dimensional structured graphene, graphene coated on the surface of active materials, and the intercalation layer stacked graphene. Through one or more of the above strategies, graphene is compounded with active substances to prepare the nanocomposite electrode, which is applied as the anode or cathode to sodium-ion batteries. The recent research progress of graphene-based nanocomposites for SIBs is also summarized in this study based on the above categories, especially for nanocomposite fabricate methods, the structural characteristics of electrodes as well as the influence of graphene on the performance of the SIBs. In addition, the relevant mechanism is also within the scope of this discussion, such as synergistic effect of graphene with active substances, the insertion/deintercalation process of sodium ions in different kinds of nanocomposites, and electrochemical reaction mechanism in the energy storage. At the end of this study, a series of strategies are summarized to address the challenges of graphene-based nanocomposites and several critical research prospects of SIBs that provide insights for future investigations

The effects of thermal annealing on the photoluminescence and DC characteristics of 1.3 µm p-doped InAs/InGaAs/GaAs quantum dot lasers

In this work, we investigated the optical characteristics of 1.3 µm p -doped InAs/InGaAs/GaAs quantum dot (QD) lasers that consist of either as-grown or annealed QDs. With reference to the as-grown QD lasers, it is found that 1) the integrated intensity of the photoluminescence could be increased by 63%, and 2) the onset of excited state lasing can be significantly delayed to a higher injection current with optimum annealing conditions. In addition, the internal quantum efficiency and internal optical loss of the annealed QD lasers has been improved. The observed improvements could be attributed to the removal of defects which act as nonradiative recombination centers in the QD structure and the reduction in the Auger-related recombination processes upon annealing

Effects of Gibberellin Pre-Treatment on Seed Germination and Seedling Physiology Characteristics in Industrial Hemp under Drought Stress Condition

The present study aimed to explore the effects of exogenous gibberellins (GAs) on seed germination and subsequent seedling growth of hemp (Cannabis sativa L.) under drought stress. Seeds of two industrial hemp cultivars i.e., ‘Yunma 1’, (YM) and ‘Bamahuoma’, (BM) were treated with different concentrations of GA3 solution (0, 200, 400, 600, 800 mg/L) at 20 °C for 8 h. The effect of pre-treatment was assessed on germination characteristics and physiological indexes on subsequent exposure to drought stress using 20% (m/v) polyethylene glycol (PEG) for 7 days. The results revealed that seed germination in hemp was sensitive to drought stress, as the germination indexes (germination rate and germination potential) decreased significantly, and seedling growth (hypocotyl length and radicle length) was impeded under 20% PEG-6000 condition. GA3 pre-treatment affected germination rate, germination potential, hypocotyl length and radicle length. With increasing GA3 concentration, these indexes first increased and then decreased. For seedling physiology characteristics in hemp, GA3-pretreatment remarkedly increased the osmotic regulating substances (soluble sugar and soluble protein contents) and the activities of antioxidant enzymes (SOD, superoxide dismutase and POD, peroxidase), while sharply decreased the lipid peroxidation (malondialdehyde, MDA) in seedlings grown under PEG-6000 induced drought stress. These results suggested that seeds pre-treated with GA3 could enhance the drought tolerance of hempseeds, and the optimal effect of GA3 for seed pre-treatment of YM and BM could be obtained when the concentration of GA3 solution reached 400 mg/L and 600 mg/L, respectively

Construction of α-MnO2 on Carbon Fibers Modified with Carbon Nanotubes for Ultrafast Flexible Supercapacitors in Ionic Liquid Electrolytes with Wide Voltage Windows

In this study, α-MnO2 and Fe2O3 nanomaterials are prepared on a carbon fiber modified with carbon nanotubes to produce the nonbinder core–shell positive (α-MnO2@CNTs/CC) and negative (Fe2O3@CNTs/CC) electrodes that can be operated in a wide voltage window in ultrafast asymmetrical flexible supercapacitors. MnO2 and Fe2O3 have attracted wide research interests as electrode materials in energy storage applications because of the abundant natural resources, high theoretical specific capacities, environmental friendliness, and low cost. The electrochemical performance of each electrode is assessed in 1 M Na2SO4 and the energy storage properties of the supercapacitors consisting of the two composite electrodes are determined in Na2SO4 and EMImBF4 electrolytes in the 2 V and 4 V windows. The 2 V supercapacitor can withstand a large scanning rate of 5000 mV S−1 without obvious changes in the cyclic voltammetry (CV) curves, besides showing a maximum energy density of 57.29 Wh kg−1 at a power density of 833.35 W kg−1. Furthermore, the supercapacitor retains 87.06% of the capacity after 20,000 galvanostatic charging and discharging (GCD) cycles. The 4 V flexible supercapacitor shows a discharging time of 1260 s and specific capacitance of 124.8 F g−1 at a current of 0.5 mA and retains 87.77% of the initial specific capacitance after 5000 GCD cycles. The mechanical robustness and practicality are demonstrated by physical bending and the powering of LED arrays. In addition, the contributions of the active materials to the capacitive properties and the underlying mechanisms are explored and discusse