Large-Signal Stability Criteria in DC Power Grids with Distributed-Controlled Converters and Constant Power Loads

The increasing adoption of power electronic devices may lead to large disturbance and destabilization of future power systems. However, stability criteria are still an unsolved puzzle, since traditional small-signal stability analysis is not applicable to power electronics-enabled power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching. To address this issue, this paper presents for the first time the rigorous derivation of the sufficient criteria for large-signal stability in DC microgrids with distributed-controlled DC-DC power converters. A novel type of closed-loop converter controllers is designed and considered. Moreover, this paper is the first to prove that the well-known and frequently cited Brayton-Moser mixed potential theory (published in 1964) is incomplete. Case studies are carried out to illustrate the defects of Brayton-Moser mixed potential theory and verify the effectiveness of the proposed novel stability criteria

Model tests of fire smoke control effects in highway tunnels

U radu je odabran tipičan tunel dužine 150 m te je izrađen njegov model u mjerilu 1:15 kako bi se ocijenili utjecaji na kontrolu dima. Na temelju Froudeovog kriterija sličnosti provedena su 32 modelska ispitivanja obrazaca širenja dima i uzdužne raspodjele temperatura. Rezultati pokazuju da na kontrolu dima utječu tri faktora i to brzina uzdužnog strujanja zraka, broj dimovodnih zaklopki i energija požara, pri čemu se smatra da na kontrolu dima najviše utječe brzina uzdužnog strujanja zraka.In this work, a typical tunnel 150 m in length is selected and modelled at a scale of 1:15 to assess its effects on smoke control. A total of 32 model tests on smoke flow pattern and longitudinal temperature distribution have been carried out based on the Froude similarity criterion. The results show that smoke control is affected by three factors, namely, the longitudinal airflow velocity, number of opened smoke-exhaust dampers, and fire power, out of which the longitudinal airflow velocity has the greatest effect on smoke control

Non-invasive detection of lymphoma with circulating tumor DNA features and protein tumor markers

BackgroundAccording to GLOBOCAN 2020, lymphoma ranked as the 9th most common cancer and the 12th leading cause of cancer-related deaths worldwide. Traditional diagnostic methods rely on the invasive excisional lymph node biopsy, which is an invasive approach with some limitations. Most lymphoma patients are diagnosed at an advanced stage since they are asymptomatic at the beginning, which has significantly impacted treatment efficacy and prognosis of the disease.MethodThis study assessed the performance and utility of a newly developed blood-based assay (SeekInCare) for lymphoma early detection. SeekInCare utilized protein tumor markers and a comprehensive set of cancer-associated genomic features, including copy number aberration (CNA), fragment size (FS), end motif, and lymphoma-related virus, which were profiled by shallow WGS of cfDNA.ResultsProtein marker CA125 could be used for lymphoma detection independent of gender, and the sensitivity was 27.8% at specificity of 98.0%. After integrating these multi-dimensional features, 77.8% sensitivity was achieved at specificity of 98.0%, while its NPV and PPV were both more than 92% for lymphoma detection. The sensitivity of early-stage (I-II) lymphoma was up to 51.3% (47.4% and 55.0% for stage I and II respectively). After 2 cycles of treatment, the molecular response of SeekInCare was correlated with the clinical outcome.ConclusionIn summary, a blood-based assay can be an alternative to detect lymphoma with adequate performance. This approach becomes particularly valuable in cases where obtaining tissue biopsy is difficult to obtain or inconclusive

Ecological filtering shapes the impacts of agricultural deforestation on biodiversity

Funding: This project was funded by the National Natural Science Foundation of China (Grants 32122057 and 3198810 to FH) and the Ministry of Science and Technology of China (Grant 2022YFF0802300 to FH), and received further support from Tsinghua University Initiative Scientific Research Program (Grant 20223080017 to LY).The biodiversity impacts of agricultural deforestation vary widely across regions. Previous efforts to explain this variation have focused exclusively on the landscape features and management regimes of agricultural systems, neglecting the potentially critical role of ecological filtering in shaping deforestation tolerance of extant species assemblages at large geographical scales via selection for functional traits. Here we provide a large-scale test of this role using a global database of species abundance ratios between matched agricultural and native forest sites that comprises 71 avian assemblages reported in 44 primary studies, and a companion database of 10 functional traits for all 2,647 species involved. Using meta-analytic, phylogenetic and multivariate methods, we show that beyond agricultural features, filtering by the extent of natural environmental variability and the severity of historical anthropogenic deforestation shapes the varying deforestation impacts across species assemblages. For assemblages under greater environmental variability—proxied by drier and more seasonal climates under a greater disturbance regime—and longer deforestation histories, filtering has attenuated the negative impacts of current deforestation by selecting for functional traits linked to stronger deforestation tolerance. Our study provides a previously largely missing piece of knowledge in understanding and managing the biodiversity consequences of deforestation by agricultural deforestation.Peer reviewe

Stability Analysis of Power-Converter-Dominated Microgrid

Power systems are going through a paradigm shift from electric machine-based to power electronics-based, with a huge number of different players on the supply side. Nowadays, thousands of distributed energy resources (DERs) are being integrated into power systems through power electronics components such as solar panels, wind turbines, and energy storage systems; however, the integration of numerous power electronic components and constant power loads (CPLs) destabilizes power systems and leads to critical oscillations. Consequently, one of the crucial challenges of this new paradigm is to keep the whole power system stable. The stability issues faced by DC microgrids are especially severe and urgent due to their unique properties. First, the low inertia of DC microgrids sharply weakens their stability; and second, owing to their advantage of smooth control, DC microgrids are unprecedentedly more promising than AC power systems given the increasing penetration of DERs. Therefore, the main purpose of this research is to solve the stability issues in power-converter-dominated DC microgrids. Considering the limited applicable ranges of traditional small-signal stability analysis, this research develops stability analysis of power-converter-dominated DC microgrids from the perspective of large-signal stability analysis. The main contributions of this research can be summarized as follows: 1) We model the DC microgrids with high penetration of power electronic devices and CPLs based on Brayton-Moser’s potential theory, including a proposed novel current-mode controller of power converters and a more realistic model of CPL. 2) We present a rigorous derivation of sufficient criteria for large-signal stability in DC microgrids with multiple power converters and CPLs. It is worth mentioning that this derivation works for many different types of power converters. In this research, the stability of each equilibrium point and the convergence of state trajectories with different starting points are discussed in detail. We integrate the discussion of the local stability of each equilibrium point into the large-signal stability analysis of the system. 3) We develop a novel approach to ROA estimation with less conservativeness using a potential-based approach. The approach tackles the common conflict between model accuracy of ROA estimation and computational overhead. 4) We resolve misunderstandings and emphasize the key points of potential theory, which plays a fundamental role in large-signal stability analysis in nonlinear power grids. Additionally, this dissertation develops a preliminary study about the microgrid control and voltage stability in AC/DC hybrid microgrids in Chapter 5, which investigates the control techniques, simulation modeling, and voltage stability analysis when a DC microgrid is connected to an AC microgrid. We will extend the preliminary study from the perspectives of stability-aware power flow management, fault detection, and grid protection in our future work.Ph.D.College of Engineering & Computer ScienceUniversity of Michigan-Dearbornhttp://deepblue.lib.umich.edu/bitstream/2027.42/174676/1/Fangyuan Chang Final Dissertation.pdfDescription of Fangyuan Chang Final Dissertation.pdf : Dissertatio

Socio-technical Transformations in Care Practices : Investigating the Implementation of Social Alarm Systems in Nursing Homes

The worldwide shortage of qualified care workers along with the increasing need for elderly care services has restrained the capacity of nursing homes to offer their residents high-quality care services. Along with digitalization, policymakers believe that technological advancements can improve the efficiency of care and streamline care work, thus helping to alleviate the challenge above. These investments include the creation of new care services by adopting innovations such as social robots, and the update of existing care services by replacing analogue technologies with digital versions, such as social alarm systems. While numerous studies have discussed the implementation of new digital technologies, the digitalization of existing care services has received less attention.This dissertation conducts empirical investigations on the digitalization of social alarm systems in four Swedish nursing homes. By applying theories of social shaping of technology with a focus on socio-technical transformations in care practices, it asks how implementation of the new social alarm systems is socially shaped in care practices. The social alarm system is an established technology that aims to enable users to call for help in emergencies. Based on a literature review of the central theme (Paper I), the dissertation examines discrepancies between planned and actual implementation outcomes (Paper II), differences within a team during project executing (Paper III), and the relationship between individuals’ actual use of technology and the assumptions inscribed in the system and the diverse care concepts in nursing homes (Paper IV). The methodological basis of the dissertation comprises analysis of implementation documents, observations of healthcare professionals’ daily work, interviews with employees of both technology companies and nursing homes, questionnaires completed by healthcare professionals, and a literature review.The results reveal that technology implementation is far from predictable outside the care context. During the implementation process, people from different groups have distinct goals, focus on different facets, and develop diverse approaches for integrating the system into daily work. Frontline professionals determine their ways of using the new social alarm system based on their personal and situational understanding of technology scripts and care concepts under given contexts. The results contribute to theoretical clarifications as well as practical possibilities and limitations to guide the implementation of social alarm systems in nursing homes. The findings indicate that the introduction of a digital social alarm system brings various changes. The digitalization of social alarm services in nursing homes can benefit from a clear positioning of the new system, a common ground for sufficient communication between actors involved, and an in-depth interpretation of local environments, as well as flexible and continuous implementation strategies.Den globala bristen på kvalificerad vårdpersonal tillsammans med det ökade behovet av äldreomsorgstjänster har begränsat vårdhemmens förmåga att erbjuda sina boende högkvalitativa vårdtjänster. Politiskt är tilltron hög till att digitaliseringen kan förbättra vårdens effektivitet, effektivisera vårdarbetet och därmed möta utmaningen med en växande äldrebefolkning. Nya vårdtjänster skapas med hjälp av digitala tillämpningar, till exempel sociala robotar, samtidigt som befintliga analoga vårdtjänster digitaliseras. Tidigare studier har framförallt fokuserat på implementeringen av helt nya digitala tekniker medan analog teknik som digitaliseras fått mindre uppmärksamhet. Avhandlingen omfattar empiriska studier av implementeringen av digitala larmsystem på fyra vårdboenden och har sitt huvudsakliga fokus på socio-tekniska förändringar i vårdens praktik, hur implementeringen av det nya larmsystemet formas socialt när den kontextualiseras. Larmsystemet är en etablerad teknik som syftar till att göra det möjligt för användare att ringa efter hjälp i nödsituationer. Baserat på en litteraturstudie (Studie I) undersöker bifogade artiklar förväntningarna på den tekniska förändringen uttryckt i roller, genomförandeplaner och strategier (Studie II); skilda uppfattningar inom ett team under genomförandet (Studie III); relationen mellan individernas faktiska teknikanvändning, de antaganden som tillskrivs tekniken från början och förekommande vårdideologi (Studie IV); samt individers roll i hanteringen av det nya systemet och vårdkulturen (Studie IV). Analysen av genomförandedokument, observationer av vårdpersonalens dagliga arbete, intervjuer med människor från både teknikföretag och vårdboenden, frågeformulär med vårdpersonal samt en litteraturöversikt bygger den metodologiska grunden för denna avhandling.Resultaten visar att ny teknik i vården är långt ifrån förutsägbar eller mätbar utanför den kontext där den implementeras. Under implementeringsprocessen har människor i organisationen olika mål, lägger vikt vid olika aspekter och har olika tillvägagångssätt för att integrera systemet i sitt arbete och sin vardag. Vårdpersonalen använder det digitala larmsystemet utifrån sin personliga och förståelse av tekniken, situationen och vården.Avhandlingens huvudsakliga bidrag handlar om teoretiska perspektiv såväl som praktiska möjligheter och begränsningar för implementeringen av sociala larmsystem på vårdboenden. Resultaten indikerar att digitaliseringen av redan kända analoga system medför olika förändringar. Digitaliseringen av larmtjänster på vårdboenden kan tjäna på en bättre kontextualisering av systemet; flexibla och kontinuerliga implementeringsstrategier; och en gemensam grund för ändamålsenlig kommunikation mellan involverade aktörer.QC 2021-11-08</p

Discrepancies between Expected and Actual Implementation: The Process Evaluation of PERS Integration in Nursing Homes

Recent studies prove that when implementing new technology technology-driven and one-size-fits-all approaches are problematic. This study focuses on the process of implementing personal emergency response system (PERS) at nursing homes. The aim is to understand why the implementation of PERS has not met initial expectations. Multiple methods were used in two Swedish nursing homes, including document analysis, questionnaires (n = 42), participant observation (67 h), and individual interviews (n = 12). A logic model was used to ascertain the discrepancies that emerged between expected and actual implementation, and the domestication theory was used to discuss the underlying meanings of the discrepancies. The discrepancies primarily focused on staff competence, system readiness, work routines, and implementation duration. Corresponding reasons were largely relevant to management issues regarding training, the procurement systems, individual and collective responsibilities as well as invisible work. The uptake of technology in daily practice is far more nuanced than a technology implementation plan might imply. We point out the importance of preparing for implementation, adjusting to new practices, and leaving space and time for facilitating implementation. The findings will be of use to implementers, service providers, and organizational managers to evaluate various measures in the implementation process, enabling them to perform technology implementation faster and more efficiently