Modeling of Self-Assembled Quantum Dot Lasers

The study of active region structure for semiconductor lasers began in the 1960s. Most recently, quantum dot (QD) based lasers have attracted increasing attention. Modeling is crucial for the design of semiconductor QD-based lasers. Many attempts have been made to the macroscopic and, particularly, the microscopic modeling of III-V semiconductor QD as well as its applications during these decades. However, these proposed approaches use a very similar but outdated way to calculate the elastic strain field, referred to as one-step model, without rigorous consideration of the influence of the growth interruption in double-capping procedure, as the latter is currently used in epitaxial self-assembly for the control over the size of QDs. This thesis aims to contribute to the design improvements of QD-based laser applications through more accurate modeling. In this thesis, we have focused on improving the modeling accuracy by elaborately analyzing the elastic strain and quantum confinement potential. By applying this accurate modeling methodology, not only the general semiconductor QD-based lasers but also the structures with an interlayer/sublayer or tightly coupled QD ensemble can be numerically modeled, giving rise to the possibility for predicting the behavior and even structural design of lasers, paving the way to potentially novel applications. The following work has been done in this thesis. Firstly, we propose an accurate method of modeling a single QD, including a thorough so-called two-step elastic strain analysis, by considering the influence of growth interruption. A series of settings in terms of the three-dimensional (3D) geometry of QD and surrounding matrix are considered. The 3D confinement potential profile is found significantly different compared with the counterpart using the conventional one-step model. The electronic band structure is then calculated by using the strain-dependent eight-band k ∙ p method. The simulation results by using the two-step model are found in better agreement than one-step model in comparison with measurements. Moreover, the impact of the quaternary compositions of barrier material is, for the first time, systematically studied. Secondly, the two-step model is further extended to three- and multi-step analysis to model the structures with additional GaP ultrathin layer above or beneath the QDs. It is found that, instead of preventing the As/P exchange, the main impact of GaP interlayer/sublayers is enhancing the quantum confinement and thereby blue-shifting the emission peak. Based on the ability to efficiently shifting the spectrum, a new vertically chirped multi-layer structure is proposed. By simultaneously optimizing the interlayer/sublayer thickness and double-capping settings, a total gain spectral bandwidth of 245.7 nm (i.e. 30% increase) is predicted, and peak wavelength is shortened to 1510 nm (i.e. 70 nm blueshift, in comparison to the case without interlayer/sublayer). Thirdly, laterally and vertically coupled QDs are modeled to investigate a variety of coupling effects in the active region of lasers. In particular, multi-step strain analysis is applied to the modeling of closely stacked QDs to reproduce a more realistic unidirectional compressive strain accumulation, evidenced by the morphological observation of cross-section images obtained from measurements. A “quasi continuum band” formed by the mixing of bonding and antibonding states is found, giving rise to the possibility of emission at excited state (ES) instead of the ground state (GS). Using this feature, a new laser structure allowing two-state lasing under continuous wave (CW) electrical pumping is proposed for the first time and characterized through the simulation of spectral linewidth and relative intensity noise (RIN). The new structure exhibits lower (i.e. −130 versus −110 dBc/Hz) integrated RIN compared with the conventional counterpart under relatively high CW current injection. Overall, this thesis sheds light on new device physics and provide guidelines to realize QD-based lasers with new features, and would be interesting to the scientific community

Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers

We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive index. This work may pave the way towards the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits

Genome-Wide Histone H3K27 Acetylation Profiling Identified Genes Correlated With Prognosis in Papillary Thyroid Carcinoma

Thyroid carcinoma (TC) is the most common endocrine malignancy, and papillary TC (PTC) is the most frequent subtype of TC, accounting for 85–90% of all the cases. Aberrant histone acetylation contributes to carcinogenesis by inducing the dysregulation of certain cancer-related genes. However, the histone acetylation landscape in PTC remains elusive. Here, we interrogated the epigenomes of PTC and benign thyroid nodule (BTN) tissues by applying H3K27ac chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) along with RNA-sequencing. By comparing the epigenomic features between PTC and BTN, we detected changes in H3K27ac levels at active regulatory regions, identified PTC-specific super-enhancer-associated genes involving immune-response and cancer-related pathways, and uncovered several genes that associated with disease-free survival of PTC. In summary, our data provided a genome-wide landscape of histone modification in PTC and demonstrated the role of enhancers in transcriptional regulations associated with prognosis of PTC

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Pleiotropic Impacts on Breast Cancer Occurrence, Development, and Therapy

Breast cancer (BC) is one of the most devastating cancers, with high morbidity and mortality, among the female population worldwide. In BC, mesenchymal stem cells (MSCs), as pluripotent stromal stem cells, play a significant role in TME formation and tumor progression. Recently, an increasing number of studies have demonstrated that extracellular vesicles (EVs) are essential for the crosstalk between MSCs and BC cells. MSC-derived EVs (MSC-EVs) can deliver a diversity of molecules, including lipids, proteins, and nucleic acids, etc., to target cells, and produce corresponding effects. Studies have demonstrated that MSC-EVs exert both inhibitory and promotive effects in different situations and different stages of BC. Meanwhile, MSC-EVs provide novel therapeutic options for BC, such as EVs as carriers for drug delivery. Therefore, in this review, we summarize the role of MSC-EVs in BC progression and application in clinical treatment, in the hope of providing a basis for further research

Comparison of three frailty scales for prediction of prolonged postoperative ileus following major abdominal surgery in elderly patients: a prospective cohort study

Abstract Background To determine whether frailty can predict prolonged postoperative ileus (PPOI) in older abdominal surgical patients; and to compare predictive ability of the FRAIL scale, the five-point modified frailty index (mFI-5) and Groningen Frailty Indicator (GFI) for PPOI. Methods Patients (aged ≥ 65 years) undergoing major abdominal surgery at our institution between April 2022 to January 2023 were prospectively enrolled. Frailty was evaluated with FRAIL, mFI-5 and GFI before operation. Data on demographics, comorbidities, perioperative management, postoperative recovery of bowel function and PPOI occurrence were collected. Results The incidence of frailty assessed with FRAIL, mFI-5 and GFI was 18.2%, 38.4% and 32.5% in a total of 203 patients, respectively. Ninety-five (46.8%) patients experienced PPOI. Time to first soft diet intake was longer in patients with frailty assessed by the three scales than that in patients without frailty. Frailty diagnosed by mFI-5 [Odds ratio (OR) 3.230, 95% confidence interval (CI) 1.572–6.638, P = 0.001] or GFI (OR 2.627, 95% CI 1.307–5.281, P = 0.007) was related to a higher risk of PPOI. Both mFI-5 [Area under curve (AUC) 0.653, 95% CI 0.577–0.730] and GFI (OR 2.627, 95% CI 1.307–5.281, P = 0.007) had insufficient accuracy for the prediction of PPOI in patients undergoing major abdominal surgery. Conclusions Elderly patients diagnosed as frail on the mFI-5 or GFI are at an increased risk of PPOI after major abdominal surgery. However, neither mFI-5 nor GFI can accurately identify individuals who will develop PPOI. Trial registration This study was registered in Chinese Clinical Trial Registry (No. ChiCTR2200058178). The date of first registration, 31/03/2022, https://www.chictr.org.cn/

Anti-Osteoporotic Effect of Lactobacillus brevis AR281 in an Ovariectomized Mouse Model Mediated by Inhibition of Osteoclast Differentiation

Osteoporosis is a global disease characterized by weakened bone microarchitecture, leading to osteoporotic fractures. Estrogen replacement therapy is the traditional treatment for osteoporosis but carries with it an increased risk of cardiac events. In search of a safe and effective treatment, we used Lactobacillus brevis AR281, which has anti-inflammatory properties, to conduct a 7-week experiment, investigating its inhibitory effects on osteoporosis in an ovariectomized (ovx) mouse model. The results demonstrated that AR281 significantly improved bone microarchitecture and biomechanical strength in ovx mice by attenuating bone resorption. AR281 significantly decreased the critical osteoclast activator, the ratio of the receptor activator for nuclear factor kappa B (NF-&kappa;B) ligand (RANKL) to osteoprotegerin, and pro-inflammatory osteoclastogenic mediators, such as IL-1, IL-6, and IL-17, which can increase the RANKL expression. Moreover, AR281 modulated intestinal microbiota in ovx mice increased the abundance of Akkermansia, which is responsible for the improvement of gut epithelial barrier integrity. In an in vitro trial, AR281 suppressed the number of osteoclasts differentiated from the osteoclast precursor RAW264.7 cells caused by RANKL through the tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6)/NF-&kappa;B/nuclear factor of activated T cells c1 (NFATc1) pathway. Therefore, AR281 may be a natural alternative for combating osteoporosis

The reliability, correlation with clinical symptoms and surgical outcomes of dural sac cross-sectional area, nerve root sedimentation sign and morphological grade for lumbar spinal stenosis

Abstract Background No study had directly compared the reliability, correlation with clinical symptoms, and surgical outcomes of dural sac cross-sectional area (DCSA), nerve root sedimentation sign (SedSign), and morphological grade for lumbar spinal stenosis (LSS). Methods From January 2017 to December 2020, 202 patients with LSS were retrospectively analyzed. The narrowest segments were assessed via T2-weighted cross-sectional images using DCSA, morphological grade, and SedSign by two independent observers. Three classifications’ reliabilities were evaluated. Correlations between three classifications and between each of the classifications and symptoms or surgical outcomes 12 months postoperatively were evaluated. Results There were 144 males and 58 females; 23, 52, and 127 patients had the narrowest segment in L2–3, L3–4, and L4–5, respectively. The intra-observer reliability of DCSA ranged from 0.91 to 0.93, and the inter-observer reliability was 0.90. The intra-observer reliability of SedSign ranged from 0.83 to 0.85, and the inter-observer reliability was 0.75. The intra-observer reliability of morphological grade ranged from 0.72 to 0.78, and the inter-observer reliability was 0.61. Each of these classifications was correlated with the other two (P < 0.01). For preoperative symptoms, DCSA was correlated with leg pain (LP) (r =  − 0.14), Oswestry Disability Index (ODI) (r =  − 0.17), and claudication (r =  − 0.19). Morphological grade was correlated with LP (r = 0.19) and claudication (r = 0.27). SedSign was correlated with ODI (r = 0.23). For postoperative outcomes, morphological grade was correlated with LP (r =  − 0.14), and SedSign was correlated with ODI (r = 0.17). Conclusions Substantial to almost perfect intra and inter-observer reliabilities for the three classifications were found; however, these classifications had either weak correlations with symptoms and surgical outcomes or none at all. Based on our findings, using one of them without conducting other tests for LSS will have limited or uncertain value in surgical decision-making or evaluating the prognostic value

Effect of Different Salt Additions on the Flavor Profile of Fermented Ciba Pepper

Salt is a key ingredient that can both enhance the taste and extend the shelf life of fermented vegetables. However, it is important to note that excessive salt levels can have adverse effects on consumer health. This study aimed to investigate the impact of various salt additions (2%, 4%, 6%, 8%, and 10% wt/wt) on the flavor profile of fermented ciba pepper, a traditional Chinese fermented chili sauce, using gas chromatography–ion mobility spectrometry (GC-IMS) in combination with an electronic nose (E-nose). Fermented ciba pepper samples were prepared with different salt additions: 2% (LJA), 4% (LJB), 6% (LJC), 8% (LJD), and 10% (LJE) (wt/wt). The physicochemical and sensory properties of the fermented ciba pepper samples were evaluated. Sensory evaluation indicated that LJC and LJD received higher scores compared to the other groups. The total acid and amino acid nitrogen contents displayed contrasting trends with the salt additions (p < 0.05). The E-nose analysis successfully differentiated the flavor profiles of the ciba pepper samples fermented with varying salt additions. Additionally, the GC-IMS analysis identified a total of 72 volatile compounds, including 14 alcohols, 21 esters, nine aldehydes, four acids, eight ketones, three terpenes, and eight other substances. Notably, the ciba pepper samples with lower salt additions exhibited higher levels of alcohols, aldehydes, and esters. In conclusion, the addition of salt during the fermentation process significantly influenced the formation of flavor compounds in ciba pepper. This study provides valuable insights into ciba pepper fermentation with different salt additions and offers prospects for the development of low-salt fermented ciba pepper products