Power-Balancing Based Induction Machine Model for Power System Dynamic Analysis in Electromechanical Timescale

Power balance, including active and reactive power, between the system supply and the demand from induction motor loads is a potentially necessary condition for system stable operation. Motion of system states depends on the balancing of active and reactive powers. Therefore, this paper proposes an induction machine model in electromechanical timescale from a power balancing viewpoint, in which the induction motor load is modeled as a voltage vector driven by power balancing between the system supply and the demand from induction motor load, so as to describe the dynamic characteristics of induction motor loads in a physical way for power system dynamic analysis. Then a voltage magnitude-phase dynamic analysis with the proposed induction machine model is constructed. Based on the voltage magnitude-phase dynamic analysis, the characteristics of grid-connected induction motor loads are explored, and the instability mechanisms of grid-connected induction motor loads induced by a large disturbance are discussed. It is shown that the dynamic behavior of grid-connected induction motor loads can be described as the dynamic process of the terminal voltage vector driven by coupled active and reactive power balancing in different timescales. In this way, the dynamic behavior of induction motor loads in terms of voltage magnitude-phase dynamics and its physical characteristics are clearly illustrated. Time-domain simulation results are presented to validate the above analyses

An iterative algorithm for solving ill-conditioned linear least squares problems

Linear Least Squares (LLS) problems are particularly difficult to solve because they are frequently ill-conditioned, and involve large quantities of data. Ill-conditioned LLS problems are commonly seen in mathematics and geosciences, where regularization algorithms are employed to seek optimal solutions. For many problems, even with the use of regularization algorithms it may be impossible to obtain an accurate solution. Riley and Golub suggested an iterative scheme for solving LLS problems. For the early iteration algorithm, it is difficult to improve the well-conditioned perturbed matrix and accelerate the convergence at the same time. Aiming at this problem, self-adaptive iteration algorithm (SAIA) is proposed in this paper for solving severe ill-conditioned LLS problems. The algorithm is different from other popular algorithms proposed in recent references. It avoids matrix inverse by using Cholesky decomposition, and tunes the perturbation parameter according to the rate of residual error decline in the iterative process. Example shows that the algorithm can greatly reduce iteration times, accelerate the convergence, and also greatly enhance the computation accuracy

Spontaneous and continuous anti-virus disinfection from nonstoichiometric perovskite-type lanthanum manganese oxide

Viral pathogens have threatened human being׳s health for a long time, from periodically breakout flu epidemics to recent rising Ebola virus disease. Herein, we report a new application of nonstoichiometric Perovskite-type LaxMnO3 (x=1, 0.95, and 0.9) compounds in spontaneous and continuous disinfection of viruses. Perovskite-type LaxMnO3 (x=1, 0.95, and 0.9) is well-known for their catalytic properties involving oxidization reactions, which are usually utilized as electrodes in fuel cells. By utilizing superb oxidative ability of LaxMnO3 (x=1, 0.95, and 0.9), amino acid residues in viral envelope proteins are oxidized, thus envelope proteins are denatured and infectivity of the virus is neutralized. It is of great importance that this process does not require external energy sources like light or heat. The A/PR/8/34H1N1 influenza A virus (PR8) was employed as the sample virus in our demonstration, and high-throughput disinfections were observed. The efficiency of disinfection was correlated to oxidative ability of LaxMnO3 (x=1, 0.95, and 0.9) by EPR and H2-TPR results that La0.9MnO3 had the highest oxidative ability and correspondingly gave out the best disinfecting results within three nonstoichiometric compounds. Moreover, denaturation of hemagglutinin and neuraminidase, the two key envelope proteins of influenza A viruses, was demonstrated by HA unit assay with chicken red blood cells and NA fluorescence assay, respectively. This unique disinfecting application of La0.9MnO3 is considered as a great make up to current sterilizing methods especially to photocatalyst based disinfectants and can be widely applied to cut-off spread routes of viruses, either viral aerosol or contaminated fluid, and help in controlling the possibly upcoming epidemics like flus and hemorrhagic fever

Thermal behavior and kinetic study on the co-pyrolysis of biomass with polymer waste

The intrinsic smaller hydrogen to carbon (H/C) ratio for lignocellulosic biomass significantly affects the yield and production of target products. Co-pyrolyzing of biomass with hydrogen-rich chemicals or raw materials offers an alternative pathway to improve the H/C ratio of feedstock and thus upgrade the bio-oils. In this work, the co-pyrolysis of rice husk (RH) with epoxy resin (ER) was attempted, and its kinetic was comprehensively studied using the model-free and model-fitting methods. The co-pyrolysis mechanism and kinetic compensation effects were probed as well. The thermogravimetric analysis indicated that the decomposition of RH-ER blend with a weight ratio of 1:1 can be divided into three stages with heating temperatures of 27-270, 270-500, and 500-850 degrees C and corresponding mass loss of 6.86, 49.30, and 5.60%, respectively. For the model-free models applied, the activation energies (Ea) displayed an uptrend in the degree of conversion (alpha) range of 0.05-0.2 and a downtrend in alpha range of 0.2-0.6. Comparing the six methods, the Ea values from Friedman method was significantly larger than those from other models. The Flynn-Wall-Ozawa (FWO) method was more reliable with higher correlation coefficients. The obtained Ea values gradually increased from 65.06 to 159.55 kJ/mol (0.05 <= alpha <= 0.20) and then decreased to 38.32 kJ/mol (0.2 < alpha <= 0.60). The Ea values calculated based on three-dimensional diffusion (Jander equation) was comparable to that from the FWO method and could be responsible for the co-pyrolysis mechanism for RH-ER blend. An excellent linear relationship lnA = 0.2058Ea - 2.63095 can be observed, indicating that the compensation effect existed between the Ea and lnA during RH and ER co-pyrolysis. The pre-exponential factor (A) was determined as 2.9E8 min(-1) using the average Ea value of 107.48 kJ/mol. Through this study, it is expected to promote the collaborative disposal of multisource solid waste

Clinical and metabolic characteristics of endometrial lesions in polycystic ovary syndrome at reproductive age

Abstract Background We aimed to explore the clinical and metabolic characteristics in polycystic ovary syndrome (PCOS) patients with different endometrial lesions. Methods 234 PCOS patients who underwent hysteroscopy and endometrial biopsy were categorized into four groups: (1) normal endometrium (control group, n = 98), (2) endometrial polyp (EP group, n = 92), (3) endometrial hyperplasia (EH group, n = 33), (4) endometrial cancer (EC group, n = 11). Serum sex hormone levels, 75 g oral glucose tolerance test, insulin release test, fasting plasma lipid, complete blood count and coagulation parameters were measured and analyzed. Results Body mass index and triglyceride level of the EH group were higher while average menstrual cycle length was longer in comparison with the control and EP group. Sex hormone-binding globulin (SHBG) and high density lipoprotein were lower in the EH group than that in the control group. 36% of the patients in the EH group suggested obesity, higher than the other three groups. Using multivariant regression analysis, patients with free androgen index > 5 had higher risk of EH (OR 5.70; 95% CI 1.05–31.01), while metformin appeared to be a protective factor for EH (OR 0.12; 95% CI 0.02–0.80). Metformin and hormones (oral contraceptives or progestogen) were shown to be protective factors for EP (OR 0.09; 95% CI 0.02–0.42; OR 0.10; 95% CI 0.02–0.56). Hormones therapy appeared to be a protective factor for EC (OR 0.05; 95% CI 0.01–0.39). Conclusion Obesity, prolonged menstrual cycle, decreased SHBG, and dyslipidemia are risk factors for EH in patients with PCOS. Oral contraceptives, progestogen and metformin are recommended for prevention and treatment of endometrial lesions in PCOS patients

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level

Additional file 1: of The prognostic value of the preoperative c-reactive protein/albumin ratio in ovarian cancer

ROC analysis of CA-125 to predict an “optimal” cutoff value (AUC area under the curve). (TIFF 23 kb