2,073 research outputs found

    Isotope reconstructions of East Asian Monsoon behaviour across Glacial Terminations I and II from Lake Suigetsu, Japan (IAP2−18−54)

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    Understanding the response of the East Asian Monsoon to rising temperatures is crucial in light of recent anthropogenic climate change and the vulnerability of East Asia to future climatic hazards. However, East Asian Monsoon dynamics during warming periods in the late Quaternary are poorly understood, particularly on decadal to millennial timescales. Significant sources of this uncertainty are the spatially and temporally heterogeneous responses of the East Asian Monsoon to submillennial temperature fluctuations. The conflicting patterns observed in available reconstructions of East Asian Monsoon strength suggest that the teleconnections acting during these intervals were complex. Understanding the behaviours of the East Asian Monsoon by accounting for links to remote climatic perturbations allows for a more holistic understanding of deglacial climate changes. A means of tackling this ambiguity is by contributing well−dated, high−resolution records of East Asian Monsoon evolution spanning Glacial Terminations I and II (which typify accessible, contrasting examples of rapid global warming) to the growing network of reconstructions from across the region. The aim of this thesis is to deconvolve East Asian Monsoon evolution during the last two glacial terminations by utilising the unique hydrological distribution of East Asian Monsoon precipitation over Japan to reconstruct both seasonal modes of the system (i.e., the East Asian Winter Monsoon and East Asian Summer Monsoon). This aim is met by the construction of isotope−based, season−specific East Asian Monsoon records across Glacial Terminations I and II using materials from the Lake Suigetsu sediment cores. This thesis is comprised of four interconnected research papers, preceded by an introduction and succeeded by a summary of findings, discussion of relevance, suggestions for future work and conclusions. In the first research paper, we utilise extended contemporary monitoring of the stable isotope composition of precipitation, river water and lake water in the Lake Suigetsu catchment to understand the factors affecting these variables and aid robust interpretation of isotope−based proxy reconstructions from the Lake Suigetsu sediment cores. Our results show that the composition of precipitation was influenced by the dual East Asian Monsoon system, and that these signals were then transferred to the lake system where they were combined with secondary local influences on lake water composition. Based on our knowledge of late Quaternary catchment dynamics, these observations suggest that the palaeo−isotope composition of Lake Suigetsu was closely related to the East Asian Monsoon. In the second research paper, we examine the influence of remote climatic processes on the East Asian Winter Monsoon and East Asian Summer Monsoon in Japan during Glacial Termination I by reconstructing trends in the strength of each seasonal mode. This is achieved using oxygen isotope analysis of diatom silica and compound−specific hydrogen isotope analysis of n−alkanoic acids from the Lake Suigetsu sediment cores. Our results support distinctive seasonal behaviours of the East Asian Monsoon during Glacial Termination I, with evidence for East Asian Winter Monsoon weakening and East Asian Summer Monsoon strengthening. The East Asian Summer Monsoon also exhibited variations in strength which were synchronous with Antarctic temperature fluctuations after 16,000 years ago, which supports a temporally restricted climatic link between Japan and the Southern Hemisphere at this time. In the third research paper, we reconstruct the East Asian Summer Monsoon in Japan during Glacial Termination II, and contrast the findings to those from Glacial Termination I. The reconstruction presented in this chapter, which is based on compound−specific hydrogen isotope analysis of n−alkanoic acids, provides evidence for early East Asian Summer Monsoon strengthening followed by a gradual weakening phase with submillennial−scale variability. Comparison of this record to others derived from mainland China supports the assertion that East Asian Summer Monsoon behaviours during Glacial Termination II were spatially heterogenous. Additionally, the different evolutions of the East Asian Summer Monsoon during Glacial Terminations I and II indicate that the system operated distinctively under contrasting boundary conditions, although the new reconstructions from Japan were consistently more closely linked with Southern Hemisphere (Antarctic) temperatures than Northern Hemisphere (Greenlandic) temperatures during both intervals. The fourth research paper was motivated by a lack of an absolute chronology for the oldest (pre−50,000 years ago) parts of the Lake Suigetsu sediment cores (which includes Glacial Termination II). In this paper, we appraise the luminescence characteristics of the cores using rapid profiling techniques. These are employed across four key time periods in order to assess the application of these methods for the detection of local and environmental shifts, and to assess the suitability of the core materials for luminescence dating. We show that the luminescence characteristics of the cores were susceptible to a range of environmental perturbations, best illustrating local changes by using high−resolution contiguous sampling. The feasibility of future luminescence dating is supported by quantifiable luminescence signals, and first order approximate ages suggest that blue light optically stimulated luminescence dating of feldspar provides the most accurate and most practical assessment of burial age. This technique should be the subject of dating efforts in pursuit of refinements to the Suigetsu core chronology before 50,000 years ago. The findings of this thesis contribute to our collective knowledge of East Asian Monsoon behaviours during glacial terminations. Critically, they represent a geographical expansion of the regional high−resolution record network to include Japan. The value of this process is demonstrated by the decoupled evolutions of each seasonal mode during Glacial Termination I, and a remote link between Antarctic temperatures and East Asian Summer Monsoon evolution in Japan during Glacial Terminations I and II, which were hitherto unconstrained by high resolution analysis. These findings acknowledge and begin to rationalise spatial and temporal heterogeneities in East Asian Monsoon behaviours by comparison to other records. This work highlights the complexity of the East Asian Monsoon, and the value of long records from contrasting deglacial periods for a better comprehension of this system in the context of anthropogenic climate change

    Redefining Disproportionate Arrest Rates: An Exploratory Quasi-Experiment that Reassesses the Role of Skin Tone

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    The New York Times reported that Black Lives Matter was the third most-read subject of 2020. These articles brought to the forefront the question of disparity in arrest rates for darker-skinned people. Questioning arrest disparity is understandable because virtually everything known about disproportionate arrest rates has been a guess, and virtually all prior research on disproportionate arrest rates is questionable because of improper benchmarking (the denominator effect). Current research has highlighted the need to switch from demographic data to skin tone data and start over on disproportionate arrest rate research; therefore, this study explored the relationship between skin tone and disproportionate arrest rates. This study also sought to determine which of the three theories surrounding disproportionate arrests is most predictive of disproportionate rates. The current theories are that disproportionate arrests increase as skin tone gets darker (stereotype threat theory), disproportionate rates are different for Black and Brown people (self-categorization theory), or disproportionate rates apply equally across all darker skin colors (social dominance theory). This study used a quantitative exploratory quasi-experimental design using linear spline regression to analyze arrest rates in Alachua County, Florida, before and after the county’s mandate to reduce arrests as much as possible during the COVID-19 pandemic to protect the prison population. The study was exploratory as no previous study has used skin tone analysis to examine arrest disparity. The findings of this study redefines the understanding of the existence and nature of disparities in arrest rates and offer a solid foundation for additional studies about the relationship between disproportionate arrest rates and skin color

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Heterogeneous Federated Learning: State-of-the-art and Research Challenges

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    Federated learning (FL) has drawn increasing attention owing to its potential use in large-scale industrial applications. Existing federated learning works mainly focus on model homogeneous settings. However, practical federated learning typically faces the heterogeneity of data distributions, model architectures, network environments, and hardware devices among participant clients. Heterogeneous Federated Learning (HFL) is much more challenging, and corresponding solutions are diverse and complex. Therefore, a systematic survey on this topic about the research challenges and state-of-the-art is essential. In this survey, we firstly summarize the various research challenges in HFL from five aspects: statistical heterogeneity, model heterogeneity, communication heterogeneity, device heterogeneity, and additional challenges. In addition, recent advances in HFL are reviewed and a new taxonomy of existing HFL methods is proposed with an in-depth analysis of their pros and cons. We classify existing methods from three different levels according to the HFL procedure: data-level, model-level, and server-level. Finally, several critical and promising future research directions in HFL are discussed, which may facilitate further developments in this field. A periodically updated collection on HFL is available at https://github.com/marswhu/HFL_Survey.Comment: 42 pages, 11 figures, and 4 table

    T Follicular Helper cell dynamics in response to vaccination

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    High quality long lived humoral immune responses require significant help from T follicular helper (Tfh) cells located within the germinal centres (GC) of lymph nodes (LN). Cognate interactions established between Tfh cells and GC B cells regulates somatic hypermutation and affinity maturation, determining the quality of antibodies produced. However, the anatomically protected location of Tfh cells, within the LN, poses a significant logistical and ethical obstacle to in vivo interrogation in humans. This study utilised the fine needle biopsy (FNB) technique to directly probe the GCs of human axillary LNs pre- and post- seasonal influenza vaccination, with the aim to interrogate the commitment of CD4+ T cells to the Tfh cell lineage. In this study, peripheral blood and draining and contralateral LN FNBs were collected prior to and 5 days post vaccination. Ex vivo phenotyping of LN FNB samples revealed significant expansion of GC Tfh cells was restricted to draining LNs. This early expansion of GC Tfh cells was characterised by an increase in highly activated, motile, and proliferating cells, measured by CD38, ICOS and Ki67 expression. Further, although no significant increase in the absolute number of Pre Tfh cells was observed, there was an increase in CD38+ICOS+ Pre-Tfh cells post vaccination, implicating this population in the immune response and highlighting the changes in cellular profile. Characterisation of cellular subsets by traditional flow cytometry techniques is limited by the number of parameters available on the instrument. Therefore, we leveraged Smart-Seq2 single cell RNA-sequencing (scRNA-seq) to further examine the heterogeneity within GC Tfh and Pre-Tfh cells. In 3 participants, we identified 7 functionally distinct clusters of cells based on differentially expressed (DE) genes. A proliferating cluster and a motile cluster were observed in all participants. The proliferating cluster exhibited an activated, proinflammatory gene signature and was enriched for Tfh differentiation gene pathways, whereas the motile cluster was enriched for pathways involved in cellular migration and motility, critical for rapid reorganisation of GCs to support dynamic interactions and cellular reactivation. To explore functional flexibility and plasticity of LN GC Tfh and Pre-Tfh, we integrated scRNAseq post vaccination data from 5 participants. Based on DE genes, we identified 5 distinct clusters; Resting, Activated migrating, B cell interacting Tfh, Proliferating and Cytotoxic. Trajectory analysis using inferred pseudotime revealed the transition of cells through activation states and the gain/loss of different CD4+ T cell lineage attributes and effector functions. Using the T cell receptor as a natural cellular barcode, we were able to identify divergent differentiation into different fate lineages from a common precursor cell. Overall, the work presented in this thesis is the first to quantify the selective activation of GC Tfh and Pre-Tfh and provides exciting and promising initial evidence of the functional heterogeneity and plastic potential with the Tfh lineage in vivo in human axillary LNs in response to vaccination, that could be leveraged to develop more effective vaccines

    20th SC@RUG 2023 proceedings 2022-2023

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    Implicit Loss of Surjectivity and Facial Reduction: Theory and Applications

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    Facial reduction, pioneered by Borwein and Wolkowicz, is a preprocessing method that is commonly used to obtain strict feasibility in the reformulated, reduced constraint system. The importance of strict feasibility is often addressed in the context of the convergence results for interior point methods. Beyond the theoretical properties that the facial reduction conveys, we show that facial reduction, not only limited to interior point methods, leads to strong numerical performances in different classes of algorithms. In this thesis we study various consequences and the broad applicability of facial reduction. The thesis is organized in two parts. In the first part, we show the instabilities accompanied by the absence of strict feasibility through the lens of facially reduced systems. In particular, we exploit the implicit redundancies, revealed by each nontrivial facial reduction step, resulting in the implicit loss of surjectivity. This leads to the two-step facial reduction and two novel related notions of singularity. For the area of semidefinite programming, we use these singularities to strengthen a known bound on the solution rank, the Barvinok-Pataki bound. For the area of linear programming, we reveal degeneracies caused by the implicit redundancies. Furthermore, we propose a preprocessing tool that uses the simplex method. In the second part of this thesis, we continue with the semidefinite programs that do not have strictly feasible points. We focus on the doubly-nonnegative relaxation of the binary quadratic program and a semidefinite program with a nonlinear objective function. We closely work with two classes of algorithms, the splitting method and the Gauss-Newton interior point method. We elaborate on the advantages in building models from facial reduction. Moreover, we develop algorithms for real-world problems including the quadratic assignment problem, the protein side-chain positioning problem, and the key rate computation for quantum key distribution. Facial reduction continues to play an important role for providing robust reformulated models in both the theoretical and the practical aspects, resulting in successful numerical performances

    Identifying Qatar's Potential for Carbon Sequestration

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    The following research collects data on the current dissemination of carbon sequestration and storage and utility (CCSU) globally, analyses the challenges of CO2 management in the long-term, as well as locates the opportunities of such technologies for the context of specific countries, in this case being Qatar. The author first defines different types of CO2 sequestration technology, measures their global advancement and other key characteristics. The study primarily utilises a systematic review methodology to identify the latest trends in CCSU, as well as analysing current technological, socio-economic, and political conditions using publicly available sources. Then, highlight findings from the literature review are compiled into a survey, aimed at specifically targeted specialist professionals in the CCSU industry who can provide input about the applicability of said CCSU solutions to Qatar. This triangulated methodology is taken forward to a deeper analysis chapter which combines desktop and survey information for a pragmatic unionisation of the study topics. This analysis includes specific suitability analysis of technologies for Qatar, current initiatives, as well as providing insight on how identified systems can be integrated for an infrastructure level carbon sequestration system. In the fifth Discussion chapter, analysis findings are critically examined for feasibility in relation to their economic feasibility in comparison to current environmental socioeconomic drivers, i.e., the vital economic output of the country’s dependence on the oil and gas sector, political threats from international relations and global climate change, as well as the lack of sustainable food and water sources in Qatar

    20th SC@RUG 2023 proceedings 2022-2023

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    Investigating Digital Corporate Reporting from an Upper Echelons Theory Perspective: Evidence from the Arab Middle East

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    Utilising the insights of Upper Echelons Theory (UET) and bounded rationality assumption, this original study aimed to investigate the association between corporate leaders’ characteristics and both the extent and readability of Digital Corporate Reporting (DCR). Content analysis of corporate websites of 122 publicly listed Jordananian firms has been carried out. The logistics regression analysis revealed that maintaining a functioning corporate website is inversely associated with CEO age. This indicates that younger CEOs are more likely to retain a web presence for the firm than their older counterparts. The OLS regression analysis revealed that CEOs’ education and tenure were negatively associated with the extent of DCR. Moreover, it was found that Corporate Governance (CG) moderating variables hardly lessen this relationship. The results confirm the current thoughts regarding the rise of CEO effects in corporations with unique evidence from the Arab Middle East (AME). Building on the previous evidence, the study also aimed at uncovering the association between chairman characteristics and the readability of the digital version of the chairman’s Letter to Shareholders (LTS). A hand-built dataset from a sample of 379 LTS from 101 publicly listed firms in 7 AME countries over five years (2014 – 2018) were employed to achieve this objective. Focusing on the clarity of DCR, the results of this second part of this study emphasizes the potential of UET to provide incremental plausible explanations of the variance in the levels of readability of LTS. The clustered regression results of the panel data demonstrate that older and less educated chairpersons are associated with more readable disclosures. Such findings on disclosure styles demonstrate the power of individuals in positions of authority as a consequence of higher education and tenure. Such findings contribute to the evolving inquiry on the significance of readability for enhancing corporate disclosure transparency and have implications for improving the DCR extent and readability
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