Analysis of subsynchronous resonance in power systems

Three aspects of Subsynchronous Resonance (SSR) related problems in power systems are addressed in this dissertation which aims at contributing to a better understanding of these problems. Subsynchronous Resonance (SSR) problems in series compensated steam-turbine power systems co-exist with the beneficial effects provided by the series capacitors. Since the early 1930s, numerous researchers have addressed issues relating to these problems. The development of a generalized frequency scan method for analyzing SSR in a Single-Machine Infinite-Bus (SMIB) power system equipped with fixed series capacitor compensation is presented. This method overcomes shortcomings present in the traditional frequency scan technique which is widely used in power system analysis. It has been noticed that there are nonlinear dynamic phenomena in power systems which can not be explained by linear system theory. This includes limited oscillations in a power system when it experiences SSR at a frequency close to one of the system modes. The phenomenon can be explained by Hopf bifurcations. This dissertation presents an analysis for a high dimensional model of a SMIB power system equipped with fixed series capacitor compensation. The results obtained can lead to a more precise understanding of this phenomenon than those available to date which use perturbation methods and highly simplified second-order power system models. Compared with fixed series capacitor compensation in power systems, the newly developed Thyristor Controlled Series Compensation (TCSC) scheme has some well known advantages with regard to flexible power system control. It has been noted that vernier mode TCSC operation can provide for SSR mitigation. In this thesis, such beneficial effect is demonstrated and analyzed for a simplified North-Western American Power System (NWAPS) model, based on EMTP simulations. Issues relating to modelling and simulation of power system and TCSC are addressed

Left-behind experience and language proficiency predict narrative abilities in the home language of Kam-speaking minority children in China

IntroductionStudies have documented that child experiences such as external/environmental factors as well as internal factors jointly affect acquisition outcomes in child language. Thus far, the findings have been heavily skewed toward Indo-European languages and children in the Western, educated, industrialized, rich and democratic (WEIRD) societies. By contrast, this study features an understudied minority language Kam, and a group of so-called left-behind children in China growing up in a unique social-communicative environment.MethodsFifty-five bilingual children aged 5–9 acquiring Kam as home language were assessed using the Multilingual Assessment Instrument for Narratives (LITMUS MAIN). Twenty-three “two parents-left” children (mean age = 6;8, range: 5;0–9;2) remained in rural areas while both parents went to cities for employment, and they were raised by their grandparents. Thirty-two were “one parent-left” peers (mean age = 7;3, range: 5;0–9;3) who also resided in rural areas but were raised by one parent. Oral narrative texts were analysed for macrostructure based on story structure (SS), story complexity (SC) and internal state terms (IS). The study examined whether and how narrative production is predicted by internal factors such as chronological age and linguistic proficiency of a child and an external factor such as left-behind experience. Four measures were scored as outcome measures: SS, SC, IS type, IS token. Four measures were taken as predictors: chronological age, left-behind experience, scores in a lexical production task, and scores in a sentence repetition task tapping expressive morphosyntactic competence.ResultsResults showed that left-behind experience consistently predicted all four outcome measures, where the “two parents-left” children scored significantly lower than their “one parent-left” peers. Expressive vocabulary scores predicted three measures: SS, SC, and IS Token. Expressive morphosyntactic scores predicted SS and SC. Age, by contrast, did not predict any outcome measure.DiscussionThese findings suggested that being left-behind by both parents may be a negative prognostic indicator for the development and maintenance of heritage language abilities in ethnic minority children. We further discussed the conceptual significance of what it means for a child to be left-behind, by relating to more basic external factors in language development, including caregiver educational level, and amount of home language and literacy support by the caretakers

Serum Sodium Concentration in Patients with Portal Hypertension and Acute Gastrointestinal Bleeding Treated with Terlipressin: A Retrospective Observational Study

This retrospective observational study aimed to investigate the risk of serum sodium concentration in patients treated with terlipressin and attempted to explore the factors associated with serum sodium concentration. We included 17 patients with portal hypertension treated with terlipressin (Group 1), 7 with portal hypertension treated with somatostatin/octreotide (Group 2), 20 with acute non-variceal gastrointestinal bleeding treated with somatostatin/octreotide (Group 3), and 19 with acute pancreatitis treated with somatostatin/octreotide (Group 4). In all groups, serum sodium concentration at baseline was not significantly different from the lowest value during the infusion of terlipressin, somatostatin, or octreotide (Group 1: 136.95 ± 4.68 versus 135.52 ± 4.79, p = 0.426; Group 2: 139.64 ± 3.86 versus 138.41 ± 5.34, p = 0.813; Group 3: 138.02 ± 4.08 versus 137.69 ± 3.11, p = 0.630; Group 4: 135.96 ± 6.87 versus 134.60 ± 3.40, p = 0.098). The rate of serum sodium concentration reduction in Group 1 (8/17) was not significantly different from Group 2 (3/7, p = 1.000), Group 3 (11/20, p = 0.746), or Group 4 (14/19, p = 0.171). Age, sex, baseline MELD and Child-Pugh scores, cDDD value and duration of terlipressin, blood transfusion, and diuretics and paracentesis during terlipressin were not significantly associated with serum sodium concentration reduction in Group 1. In conclusion, serum sodium concentration is often reduced in patients treated with terlipressin. However, the association of sodium concentration reduction with terlipressin should be clarified

Plasmonic nanoparticles assemblies templated by helical bacteria and resulting optical activity

Plasmonic nanoparticles (NPs) adsorbing onto helical bacteria can lead to formation of NP helicoids with micron scale pitch. Associated chiroptical effects can be utilized as bioanalytical tool for bacterial detection and better understanding of the spectral behavior of helical self‐assembled structures with different scales. Here, we report that enantiomerically pure helices with micron scale of chirality can be assembled on Campylobacter jejuni, a helical bacterium known for severe stomach infections. These organisms have right‐handed helical shapes with a pitch of 1–2 microns and can serve as versatile templates for a variety of NPs. The bacteria itself shows no observable rotatory activity in the visible, red, and near‐IR ranges of electromagnetic spectrum. The bacterial dispersion acquires chiroptical activity at 500–750 nm upon plasmonic functionalization with Au NPs. Finite‐difference time‐domain simulations confirmed the attribution of the chiroptical activity to the helical assembly of gold nanoparticles. The position of the circular dichroism peaks observed for these chiral structures overlaps with those obtained before for Au NPs and their constructs with molecular and nanoscale chirality. This work provides an experimental and computational pathway to utilize chiroplasmonic particles assembled on bacteria for bioanalytical purposes.Gold nanoparticles assemble onto the surface of helical bacterium, Campylobacter jejuni, producing right‐handed helices with a pitch of 1–2 microns. The bacterial dispersion acquires chiroptical activity at 500–750 nm that matches the calculated chiroplasmonic spectra. This study provides a pathway to utilize chiroplasmonic particles for monitoring shape dynamics of bacteria and identification of helical bacteria in complex microbiomes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155927/1/Supporting_information_Chirality_Manuscript_2020.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155927/2/chir23225_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155927/3/chir23225.pd

Two-dimensional mapping of residual stresses in a thick dissimilar weld using contour method, deep hole drilling, and neutron diffraction

Residual stress variations were determined through the thickness of a 70-mm-thick ferritic–austenitic dissimilar steel weld using contour method, deep hole drilling, and neutron diffraction. The result shows that significant tensile stresses were distributed distinctly along the interface between ferritic and austenitic phases. The band of the large tensile stresses was about 8 mm wide and the magnitude reached 400 MPa, which is approaching 100 % of the yield strength of the base metal, near the top surface (about 15 % of the depth). It is attributed to the large difference (5.8 × 10−6 1/°C) of the thermal expansion coefficient between ferritic and austenitic steels of the interface. The microstructure analysis elucidates that the martensitic phase prevailed near the interface and results in microhardness increases

Caffeine intake and anxiety: a meta-analysis

The results from studies on relationship between caffeine intake and risk of anxiety remains controversial, so we conducted a meta-analysis to summarize the evidence about the association between caffeine intake and risk of anxiety. Relevant articles were identified by researching PubMed, Web of Science, Cochrane library, Embase, CNKI, WANFANG DATA, SinoMed and VIP from the inception to December, 2022. Three investigators independently sifted through the literature, extracted the data, and evaluated the quality of the included studies based on predetermined selection criteria and assessed articles with Risk of bias assessment tool for Cochrane systematic reviews and analytical cross-sectional study quality assessment tool from JBI PACES. After assessing the quality of the literature, meta-analysis was performed using Revman 5.4 and Stata 12.0. Data were obtained from eight articles, and 546 participants from 14 studies in eight articles from healthy populations were included in the caffeine-anxiety analyses. As the scales used to assess anxiety vary in the literature, we chose standardized mean difference as the outcome indicator. In terms of overall effect, the results of the meta-analysis showed that caffeine intake increased the risk of anxiety [SMD = 0.94, 95% Cl = (0.28, 1.60), p < 0.05]. After suspecting that dose size might be responsible for the heterogeneity by sensitivity analysis, we performed subgroup analysis according to dose size and found that low-dose caffeine intake moderately increased the risk of anxiety [SMD = 0.61, 95%Cl = (0.42, 0.79), p < 0.05], whereas high-dose caffeine intake had a highly significant increase in the risk of anxiety [SMD = 2.86, 95%Cl = (2.50, 3.22), p < 0.05]. The results confirm that caffeine intake is associated with an elevated risk of anxiety in healthy individuals without psychiatric disorders, especially when the intake dose is greater than 400 mg

Mitochondrial DNA Leakage Caused by Streptococcus pneumoniae Hydrogen Peroxide Promotes Type I IFN Expression in Lung Cells

Streptococcus pneumoniae (S. pn), the bacterial pathogen responsible for invasive pneumococcal diseases, is capable of producing substantial amounts of hydrogen peroxide. However, the impact of S. pn-secreted hydrogen peroxide (H2O2) on the host immune processes is not completely understood. Here, we demonstrated that S. pn-secreted H2O2 caused mitochondrial damage and severe histopathological damage in mouse lung tissue. Additionally, S. pn-secreted H2O2 caused not only oxidative damage to mitochondrial deoxyribonucleic acid (mtDNA), but also a reduction in the mtDNA content in alveolar epithelia cells. This resulted in the release of mtDNA into the cytoplasm, which subsequently induced type I interferons (IFN-I) expression. We also determined that stimulator of interferon genes (STING) signaling was probably involved in S. pn H2O2-inducing IFN-I expression in response to mtDNA damaged by S. pn-secreted H2O2. In conclusion, our study demonstrated that H2O2 produced by S. pn resulted in mtDNA leakage from damaged mitochondria and IFN-I production in alveolar epithelia cells, and STING may be required in this process, and this is a novel mitochondrial damage mechanism by which S. pn potentiates the IFN-I cascade in S. pn infection