Analytical Frequency Nadir Prediction Considering Inverter-Based Fast Frequency Response

This letter develops an analytical frequency nadir prediction method that allows for the consideration of three potential forms of fast frequency response (FFR) provided by inverter-based resources. The proposed method provides fast and accurate frequency nadir estimation after N-1 generation tripping contingencies. Our method is grounded on the closed-form solution for the frequency nadir, which is solved from the second-order system frequency response model considering the governor dynamics and three types of FFR. The simulation results in the IEEE 39-bus system with different types of FFR demonstrate that the proposed method provides accurate and fast prediction for the frequency nadir under various disturbances

Analysis and realization of pathology diagnosis on intraoperative frozen sections of papillary thyroid carcinoma

目的  探讨术中冷冻切片在甲状腺肿瘤手术中的应用，提高甲状腺乳头状癌术中冷冻病理诊断的准确率。方法  回顾性观察我科43例甲状腺乳头状癌患者的术中冷冻切片。结果  术中冷冻切片诊断甲状腺乳头状癌43例，确诊率为100%。结论  为提高术中冷冻切片病理诊断的准确性，必须加强与临床医师沟通，详细了解患者的临床资料，正确全面的取材，掌握甲状腺乳头状癌的病理诊断及鉴别要点，提高冷冻切片质量。Objective:To explore the application of intraoperative frozen sections in thyroid tumor surgery and to improve its diagnostic accuracy in thyroid tumor surgery. Methods:To respectively analyze the intraoperative frozen sections of 43 cases of papillary thyroid carcinoma in our department. Results:By intraoperative frozen sections, 43 cases of papillary thyroid carcinoma were diagnosed, the diagnostic accuracy amounting to 100%.Conclusion:Increasing the diagnosis accuracy of intraoperative frozen sections counts in understanding clinical data in detail，drawing materials correctly and comprehensively，commanding common papillary thyroid carcinoma pathologic diagnosis and differentiated points，enhancing the communication with clinicians and improving the quality of frozen sections

Sox2, a stemness gene, regulates tumor-initiating and drug-resistant properties in CD133-positive glioblastoma stem cells

AbstractBackgroundGlioblastoma multiforme (GBM) is the most lethal type of adult brain cancer and performs outrageous growth and resistance regardless of adjuvant chemotherapies, eventually contributing to tumor recurrence and poor outcomes. Considering the common heterogeneity of cancer cells, the imbalanced regulatory mechanism could be switched on/off and contribute to drug resistance. Moreover, the subpopulation of GBM cells was recently discovered to share similar phenotypes with neural stem cells. These cancer stem cells (CSCs) promote the potency of tumor initiation. As a result, targeting of glioma stem cells has become the dominant way of improving the therapeutic outcome against GBM and extending the life span of patients. Among the biomarkers of CSCs, CD-133 (prominin-1) has been known to effectively isolate CSCs from cancer population, including GBM; however, the underlying mechanism of how stemness genes manipulate CSC-associated phenotypes, such as tumor initiation and relapse, is still unclear.MethodsTumorigenicity, drug resistance and embryonic stem cell markers were examined in primary CD133-positive (CD133+) GBM cells and CD133+ subpopulation. Stemness signature of CD133+ GBM cells was identified using microarray analysis. Stem cell potency, tumorigenicity and drug resistance were also tested in differential expression of SOX2 in GBM cells.ResultsIn this study, high tumorigenic and drug resistance was noticed in primary CD-133+ GBM cells; meanwhile, plenty of embryonic stem cell markers were also elevated in the CD-133+ subpopulation. Using microarray analysis, we identified SOX2 as the most enriched gene among the stemness signature in CD133+ GBM cells. Overexpression of SOX2 consistently enhanced the stem cell potency in the GBM cell lines, whereas knockdown of SOX2 dramatically withdrew CD133 expression in CD133+ GBM cells. Additionally, we silenced SOX2 expression using RNAi system, which abrogated the ability of tumor initiation as well as drug resistance of CD133+ GBM cells, suggesting that SOX2 plays a crucial role in regulating tumorigenicity in CD133+ GBM cells.ConclusionSOX2 plays a crucial role in regulating tumorigenicity in CD133+ GBM cells. Our results not only revealed the genetic plasticity contributing to drug resistance and stemness but also demonstrated the dominant role of SOX2 in maintenance of GBM CSCs, which may provide a novel therapeutic target to overcome the conundrum of poor survival of brain cancers

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Grid integration of renewable energy sources via virtual synchronous generator

Ongoing efforts toward environmentally sustainable electricity generation give rise to gradual displacement of synchronous generators by renewable energy resources (RESs). This paradigm shift reshapes power system dynamics and presents numerous challenges to reliable and efficient grid operations. For example, our power system will have reduced inertia and be at higher risk of instability, since the RESs generally interconnect to the grid via power-electronic converters with less or no inertia. Motivated by these challenges arising from RES integration, the concept of virtual synchronous generator (VSG) has been proposed to provide virtual inertia by emulating the SG dynamics in the RES controller. Among all VSG designs, synchronverter is a representative one with concise structure. However, this dissertation finds that conventional synchronverter designs lack in control degrees of freedom, require trial-and-error tuning process, synchronize with the grid slowly, and suffer from output-power coupling. Also, their active-power transfer capacity has not been studied, especially under weak-grid conditions. In order to address these problems and integrate more RESs into our system, my dissertation has five major contributions ranging from control design to tuning method to operation characteristics. First, in order to improve the synchronverter control degrees of freedom, I augment the synchronverter with a damping correction loop, which freely adjusts its response speed without affecting the steady-state performance. In order to simplify the tuning process, I propose a tuning method that evaluates the feasible pole-placement region and directly computes synchronverter parameters to achieve desired dynamics. My proposed tuning method completely avoids the trial-and-error tuning process and thus has overwhelming advantages over conventional tuning methods. Next, in order to synchronize the synchronverter quickly to the grid and enable the flexible ``plug-and-play" operation of RESs, this dissertation proposes a self-synchronizing synchronverter design with both fast self-synchronization speed and easily tuneable parameters. Then, to further improve the tracking performance, I propose a design with reduced output-power coupling. Finally, in order to integrate synchronverter-based RESs in weak grid, this dissertation analytically studies its active power transfer capacity and proposes two countermeasures to improve it. All my proposed designs and analyses are verified through extensive numerical or experimental studies.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Detection of Pirimiphos-Methyl in Wheat Using Surface-Enhanced Raman Spectroscopy and Chemometric Methods

Pesticide residue detection is a hot issue in the quality and safety of agricultural grains. A novel method for accurate detection of pirimiphos-methyl residues in wheat was developed using surface-enhanced Raman spectroscopy (SERS) and chemometric methods. A simple pretreatment method was conducted to extract pirimiphos-methyl residue from wheat samples, and highly effective gold nanorods were prepared for SERS measurement. Raman peaks assignment was calculated using density functional theory. The Raman signal of pirimiphos-methyl can be detected when the concentrations of residue in wheat extraction solution and contaminated wheat is as low as 0.2 mg/L and 0.25 mg/L, respectively. Quantification of pirimiphos-methyl was performed by applying regression models developed by partial least squares regression, support vector machine regression and random forest with principal component analysis using different preprocessed methods. As for the contaminated wheat samples, the relative deviation between gas chromatography-mass spectrometry value and predicted value is in the range of 0.10%−6.63%, and predicted recovery is 94.12%−106.63%, ranging from 23.93 mg/L to 0.25 mg/L. Results demonstrated that the proposed SERS method is an effective and efficient analytical tool for detecting pirimiphos-methyl in wheat with high accuracy and excellent sensitivity