4,580 research outputs found

    Eunomia: Enabling User-specified Fine-Grained Search in Symbolically Executing WebAssembly Binaries

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    Although existing techniques have proposed automated approaches to alleviate the path explosion problem of symbolic execution, users still need to optimize symbolic execution by applying various searching strategies carefully. As existing approaches mainly support only coarse-grained global searching strategies, they cannot efficiently traverse through complex code structures. In this paper, we propose Eunomia, a symbolic execution technique that allows users to specify local domain knowledge to enable fine-grained search. In Eunomia, we design an expressive DSL, Aes, that lets users precisely pinpoint local searching strategies to different parts of the target program. To further optimize local searching strategies, we design an interval-based algorithm that automatically isolates the context of variables for different local searching strategies, avoiding conflicts between local searching strategies for the same variable. We implement Eunomia as a symbolic execution platform targeting WebAssembly, which enables us to analyze applications written in various languages (like C and Go) but can be compiled into WebAssembly. To the best of our knowledge, Eunomia is the first symbolic execution engine that supports the full features of the WebAssembly runtime. We evaluate Eunomia with a dedicated microbenchmark suite for symbolic execution and six real-world applications. Our evaluation shows that Eunomia accelerates bug detection in real-world applications by up to three orders of magnitude. According to the results of a comprehensive user study, users can significantly improve the efficiency and effectiveness of symbolic execution by writing a simple and intuitive Aes script. Besides verifying six known real-world bugs, Eunomia also detected two new zero-day bugs in a popular open-source project, Collections-C.Comment: Accepted by ACM SIGSOFT International Symposium on Software Testing and Analysis (ISSTA) 202

    Investigating neural differentiation capacity in Alzheimer’s disease iPSC-derived neural stem cells

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    Neurodegeneration in Alzheimer’s disease (AD) may be exacerbated by dysregulated hippocampal neurogenesis. Neural stem cells (NSC) maintain adult neurogenesis and depletion of the NSC niche has been associated with age-related cognitive decline and dementia. We hypothesise that familial AD (FAD) mutations bias NSC toward premature neural specification, reducing the stem cell niche over time and accelerating disease progression. Somatic cells derived from patients with FAD (PSEN1 A246E and PSEN1 M146L heterozygous mutations) and healthy controls were reprogrammed to generate induced pluripotent stem cells (iPSC). Pluripotency for patient and control iPSC lines was confirmed, then cells were amplified and cryopreserved as stores. iPSC were subjected to neural specification to rosette-forming SOX2+/nestin+ NSCs for comparative evaluations between FAD and age-matched controls. FAD patient and control NSC were passaged under defined steady state culture conditions to assess stem cell maintenance using quantitative molecular markers (SOX2, nestin, NeuN, MAP2 and βIII-tubulin). We observed trends towards downregulated expression of the nestin coding gene NES (p=0.051) and upregulated expression of MAP2 (p=0.16) in PSEN1 NSC compared with control NSC, indicative of a premature differentiation phenotype induced by presence of the PSEN1 mutation. Cell cycle analysis of PSEN1 NSC showed that compared with controls, a greater number of PSEN1 NSC were retained in G0/G1 phase of the cell cycle (p=0.39), fewer progressed to S-phase (p=0.11) and fewer still reached G2 phase (p=0.23), suggesting cell cycle progression may be impaired in PSEN1 NSC. Nuclear DNA fragmentation was increased (p=0.10) in FAD NSC compared with controls, indicative of elevated cell death/apoptosis. Flow cytometry-based analysis of live, nestin+ NSC and NPC indicated increased apoptosis (p=0.14) in FAD NSC compared with controls, as well as increasing levels of apoptosis (p=0.33) in FAD NSC as they specified to neural progenitor cells. Global RNA sequencing was used to identify transcriptomic changes occurring during both disease and control neural specification. GO analysis of DEGs between PSEN1 and control NSC at P3 revealed significant upregulation (FDR<0.0000259) of 5 biological processes related to transcription and gene expression as well as significant upregulation (FDR<0.000000725) of 12 molecular functions related to DNA binding and transcription factor activity. These data suggest significant changes in gene expression were occurring in PSEN1 NSC at P3 compared with control NSC at the same stage in neural specification. The number of DEGs (p<0.05) between PSEN1 and control NSC at P3 was 9.92-fold higher than the number of DEGs between PSEN1 and control NSC at P2, suggesting transcriptomic differences between PSEN1 and control NSC become more pronounced as cells specify further down the neural lineage. Gene ontology (GO) analysis of differentially expressed genes (DEGs) specific to AD neural differentiation revealed significant dysregulation (FDR p<0.05) of genes related to neurogenesis, apoptosis, cell cycle, transcriptional control, and cell growth/maintenance as PSEN1 NSC matured from P2 to P3. The number of DEGs (p<0.05) in PSEN1 neural differentiation was 4.7-fold higher than the number of DEGs seen in control neural differentiation, indicating more transcriptional changes occurred in PSEN1 NSC than in controls at the same time point in neural specification. Dysregulation of Notch signalling was specific to PSEN1 neural differentiation and Notch related DEGs significantly upregulated (p<0.05) in PSEN1 NSC at P3 compared with P2 included NCOR2, JAG2, CHAC1 and RFNG. qPCR based validation displayed significant upregulation of RFNG (p=0.04) in PSEN1 NSC at P3 compared with PSEN1 NSC at P2, and indicated a trend towards upregulation of JAG2 expression, correlating with RNA sequencing data. Data generated in this study indicate that presence of the PSEN1 mutation significantly increases the number of transcriptional changes occurring during neural differentiation. It is plausible that transcriptional changes to Notch signalling cause dysregulated neural specification and increased apoptosis in PSEN1 NSC, ultimately resulting in depletion of the NSC niche

    Bayesian Forecasting in Economics and Finance: A Modern Review

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    The Bayesian statistical paradigm provides a principled and coherent approach to probabilistic forecasting. Uncertainty about all unknowns that characterize any forecasting problem -- model, parameters, latent states -- is able to be quantified explicitly, and factored into the forecast distribution via the process of integration or averaging. Allied with the elegance of the method, Bayesian forecasting is now underpinned by the burgeoning field of Bayesian computation, which enables Bayesian forecasts to be produced for virtually any problem, no matter how large, or complex. The current state of play in Bayesian forecasting in economics and finance is the subject of this review. The aim is to provide the reader with an overview of modern approaches to the field, set in some historical context; and with sufficient computational detail given to assist the reader with implementation.Comment: The paper is now published online at: https://doi.org/10.1016/j.ijforecast.2023.05.00

    ADCL: Acceleration Driven Clause Learning for Constrained Horn Clauses

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    Constrained Horn Clauses (CHCs) are often used in automated program verification. Thus, techniques for (dis-)proving satisfiability of CHCs are a very active field of research. On the other hand, acceleration techniques for computing formulas that characterize the N-fold closure of loops have successfully been used for static program analysis. We show how to use acceleration to avoid repeated derivations with recursive CHCs in resolution proofs, which reduces the length of the proofs drastically. This idea gives rise to a novel calculus for (dis)proving satisfiability of CHCs, called Acceleration Driven Clause Learning (ADCL). We implemented this new calculus in our tool LoAT and evaluate it empirically in comparison to other state-of-the-art tools

    An onto-epistemological (re)framing and (re)connecting of organisations as praxeological multi-capital value systems

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    Organisation stands as one of humankind’s greatest inventions, and reconceptualising organisations to meet the ever-diversifying needs of the modern stakeholder community one of its most significant challenges. Historically, scientific management principles simplified the challenge through a profitable operations practice imperative, which reinforced a creation and destruction value dualism, and causal and value dead ends. However, value is contingent upon meeting needs, demanding that organisations leverage a wider and connected set of capitals to meet the diverse needs of modernity. This research seeks to understand how praxeologically inert legacy organisations can generate value by (re)connecting capitals and (re)framing as multi-capital value systems. The study’s setting is the university-led Made Smarter Leadership Development programme which provided an insightful longitudinal case study over the two-year programme life-cycle. The research surfaced rich qualitative insights on participant sense-making journeys across a diverse set of participant-researcher touchpoints, and also collected associated quantitative survey data. Analysis was conducted in three streams, and iteratively built up a complementary organisational model ontology. Stream one, a qualitative ethnographic study utilised grounded theory analysis to surface the prâxis (re)framing priorities of organisations. Analysis of such priorities yielded an onto-epistemological perspective of an organisation, and novel insights were generated on prâxis (re)framing strategies, organisational maturity, and how prâxes and frames combine as a relational onto-epistemological duality. Stream two’s quantitative analysis of respondent data identified the 20 significant prâxis-elements that form six systemically correlated and causally related capital factors. Findings indicate how multiple capitals connect as an organisational structure which orchestrates value flows between capital factors. Stream three elaborated on the prior two streams’ empirically-grounded foundations through sensemaking systems dynamics theory. This modelling produced both empirical findings and a generalisable methodology to reconceptualise organisations as a connected praxeological multi-capital value system. Specifically, findings informed how means-ends dynamics orchestrate complex capital interactions, which form pan-organisational value journeys, and ultimately form generalisable value archetypes. In summary, the research confirmed an organisation is a connected multi-capital praxeological value system, this outcome enabled by the discovery of a novel onto-epistemological perspective of organisations

    Late-bound code generation

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    Each time a function or method is invoked during the execution of a program, a stream of instructions is issued to some underlying hardware platform. But exactly what underlying hardware, and which instructions, is usually left implicit. However in certain situations it becomes important to control these decisions. For example, particular problems can only be solved in real-time when scheduled on specialised accelerators, such as graphics coprocessors or computing clusters. We introduce a novel operator for hygienically reifying the behaviour of a runtime function instance as a syntactic fragment, in a language which may in general differ from the source function definition. Translation and optimisation are performed by recursively invoked, dynamically dispatched code generators. Side-effecting operations are permitted, and their ordering is preserved. We compare our operator with other techniques for pragmatic control, observing that: the use of our operator supports lifting arbitrary mutable objects, and neither requires rewriting sections of the source program in a multi-level language, nor interferes with the interface to individual software components. Due to its lack of interference at the abstraction level at which software is composed, we believe that our approach poses a significantly lower barrier to practical adoption than current methods. The practical efficacy of our operator is demonstrated by using it to offload the user interface rendering of a smartphone application to an FPGA coprocessor, including both statically and procedurally defined user interface components. The generated pipeline is an application-specific, statically scheduled processor-per-primitive rendering pipeline, suitable for place-and-route style optimisation. To demonstrate the compatibility of our operator with existing languages, we show how it may be defined within the Python programming language. We introduce a transformation for weakening mutable to immutable named bindings, termed let-weakening, to solve the problem of propagating information pertaining to named variables between modular code generating units.Open Acces

    Reframing Construction Labour Productivity in a Colonisation Context: The West Bank as an Example

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    This thesis explores the under-researched topic of defining construction labour productivity and the factors impacting it in the context of a small, volatile and dependent economy of the West Bank. The aim is to identify the impact of particular social, economic and political constraints on structural and agency factors affecting the construction sector's productivity using case studies from the West Bank. Labour productivity is studied from a broad perspective, adding political and economic conditions to reframe and evaluate the term and its determinants in the context of high uncertainty, political instability and complex geography. 'Labour productivity' comes to represent the production interplay between agency and structural factors, and construction labour is treated as complementary to the machine rather than as an extension of it. The theoretical framework is developed based on Giddens' Structuration Theory, mainly the reconciliation of the multi-layers structure and agency determinants impacting construction labour productivity in the context of colonisation. The study's philosophy validates the use of mixed methods methodology, merging positivism and constructivism under the canopy of pragmatism. Quantitative and qualitative data have been collected, with the quantitative part consisting primarily of comprehensive survey data from the PCBS and the qualitative of purposive semi-structured interviews with decision makers at macro and meso levels plus analysis of multiple case studies. The results reveal that the controversy about using hourly wage as an indication of construction productivity is resolved by including labour characteristics and context-specific variables in the model. The construction sector in Israel depends on skilled blue-collar employees from the West Bank rather than unskilled ones, with a higher rate of labour mobility for those from rural areas to Israeli construction markets than from other locations, leading to skill shortages in the West Bank. The construction labour process in the West Bank also rests on low levels of vocational education and training and a high risk of accidents due to meagre experience, lack of training and improper application of health and safety regulations. Finally, Israeli control of movement within the West Bank and the outlets to international markets impacts on labour productivity by imposing restrictions on importing and transporting construction materials and the internal mobility of workers. The research contributes to knowledge through its originality and generalisation by mapping the complexity of social factors and providing a definition of construction productivity appropriate to colonisation

    Community Radio Broadcasting and Local Governance Participation in Ghana: A Study of Simli Radio in the Kumbungu District of the Northern Region.

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    This research explores the nexus between community radio and local community participation in decentralized local governance in the Ghanaian context. It is based on a case study of the Kumbungu District in the Northern region. Ghana has implemented a local government programme under its decentralised reforms since 1988, and this was primarily aimed at stimulating the active participation of ordinary citizens in the affairs of governance and in development intervention at the local community level, yet the available evidence highlights poor community participation in district level government business. Community radio has long been established as a communication tool that amplifies marginalised voices in democratic societies that are relative to identity formation and community development. However, there are very few academic discussions that explore the contribution of community radio in addressing the concerns relating to poor local community participation in decentralized local governance in Ghana. Employing qualitative research approaches for the data collection, a key question that this research addresses is how, and why, poor local community participation and weaknesses in local accountability in the country’s decentralised reforms are linked to an inadequate flow of communication and the lack of legitimate mechanisms with which to amplify the voices of ordinary members of the community. Additionally, this research explores the question of how CR is addressing the failure of existing communication systems in the local government structures to facilitate active citizengovernment dialogue and a synergy that strengthens the articulation of community voices and enhances the responsiveness of local government policies and initiatives. The study found that the poor community participation in local governance is due to the failure of the local assembly to incorporate into their mobilisation strategies and administrative structures effective, credible and trustworthy communication systems that guarantee the best interests of the local people. The research established that the concerns relating to low community participation in local government activities in Ghana is linked to the lack of access to local government information, as the civic education campaigns of district assemblies fail to address key factors that undermine local community participation in local governance. In the particular case of Simli Radio, the research found that the station encourages creative expressions and contributes to democratic processes at the local level through participatory programming, open access to its facilities and the stimulation of the local community’s sense of identity and ownership of the station, thus enabling the local community to contribute to issues that affect their daily political and socioeconomic lives. Simli Radio’s open access allows local people to focus on local issues, giving voice to groups and individuals who otherwise would not have had the opportunity to express their views, to hold local authority leaders accountable and to act in the best interests of the local community
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