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Item
Open Access
Secure Smart Contract-based Computation (Verifiable computation, Fair two-party protocols, and Resource sharing)
(2024-02-15) Avizheh, Sepideh; Safavi-Naini, Reihaneh; Jacobson Jr., Michael John; Henry, Ryan; Far, Behrouz; Pieprzyk, Josef
A smart contract is a trusted computer program that runs on the decentralized computer that underlies a blockchain. Smart contracts are part of Web3 technology, the next generation of the Internet, and they enable distributed applications over the Internet. Smart contracts can remove intermediaries in real-world systems and have the promise of revolutionizing industries and processes in healthcare, retail, banking, government, and many more. Because of their trusted execution, smart contracts have been used as a trusted third party/referee in cryptographic protocols. They have also been used to automate processes and seamlessly incorporate cryptocurrency in payments. In this thesis, we consider the application of the smart contract as a trusted (semi-honest) third party/referee in the following problems: verifiable computation using refereed delegation of computation, fair two-party protocols that include fair private set intersection and fair exchange, and resource sharing. We show that the direct replacement of the trusted third party/referee with the smart contract can expose the protocols to new threats and attacks. We model the security of each protocol, analyze the security of the existing ones, propose new protocols that can achieve the required security guarantee in the smart contract setting, provide a proof-of-concept implementation, and evaluate their performance. Our results incorporate both secure smart contract-based cryptographic protocols and systems. We mainly propose formal models and descriptions in the real-world/ideal-world paradigm for the cryptographic protocols. We also look into the privacy in the smart contract setting. The smart contract is transparent and interactions with the smart contract are through public communication channels, thus ensuring the privacy of the parties' input and messages becomes a significant challenge in designing the protocols. We lay the foundations to define and capture privacy for a smart contract and use it to show the privacy of our cryptographic protocols.
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Open Access
Performance of multistage-fractured horizontal wells with secondary discrete fractures in heterogeneous tight reservoirs
(2024-02-13) Deng, Qi; Qu, Jianhua; Mi, Zhongrong; Xu, Bing; Lv, Xindong; Huang, Kai; Zhang, Boning; Nie, Ren-Shi; Chen, Shengnan
Abstract A significant portion of tight sandstone reservoirs commonly displays intricate fluvial channels or fault systems. Despite various attempts at analytical/semi-analytical modeling of multistage-fractured horizontal wells (MFHWs) in unconventional reservoirs, the majority of studies have focused on scenarios with homogeneous original physical properties, neglecting cases where MFHWs traverse multiple regions in channelized heterogeneous reservoirs. Comprehending the influence of heterogeneous and leaky faults on the performance of MFHWs is essential for efficient development. This study presents an innovative semi-analytical model to analyze the pressure transient behavior of MFHWs with secondary fractures as they traverse multiple regions in banded channel heterogeneous reservoirs, particularly considering the presence of partially-communicating faults. The approach combines the source method and Green’s function method to obtain solutions, introducing a novel technique for discretizing fractures without discretizing interfaces. The effects of the reservoir heterogeneity, partially-communicating faults and fractures system on pressure behavior are analyzed. The results indicate that the pressure behavior of MFHWs passing through regions with different physical properties exhibits distinctive characteristics, differing from both the homogeneous case and the heterogeneous cases where the well does not traverse distinct regions. Permeability heterogeneity influences the curves of all other flow regimes, except the early and late flow regimes. Faults affect transient pressure behavior only when not positioned in the middle of each two primary fractures. Region area heterogeneity primarily influences the medium flow regimes. This work provides valuable insights into the performance of MFHWs in channelized heterogeneous reservoirs, offering technical support for well testing in these reservoirs.
Item
Open Access
Performance of multistage-fractured horizontal wells with secondary discrete fractures in heterogeneous tight reservoirs
(2024-02-13) Deng, Qi; Qu, Jianhua; Mi, Zhongrong; Xu, Bing; Lv, Xindong; Huang, Kai; Zhang, Boning; Nie, Ren-Shi; Chen, Shengnan
Abstract A significant portion of tight sandstone reservoirs commonly displays intricate fluvial channels or fault systems. Despite various attempts at analytical/semi-analytical modeling of multistage-fractured horizontal wells (MFHWs) in unconventional reservoirs, the majority of studies have focused on scenarios with homogeneous original physical properties, neglecting cases where MFHWs traverse multiple regions in channelized heterogeneous reservoirs. Comprehending the influence of heterogeneous and leaky faults on the performance of MFHWs is essential for efficient development. This study presents an innovative semi-analytical model to analyze the pressure transient behavior of MFHWs with secondary fractures as they traverse multiple regions in banded channel heterogeneous reservoirs, particularly considering the presence of partially-communicating faults. The approach combines the source method and Green’s function method to obtain solutions, introducing a novel technique for discretizing fractures without discretizing interfaces. The effects of the reservoir heterogeneity, partially-communicating faults and fractures system on pressure behavior are analyzed. The results indicate that the pressure behavior of MFHWs passing through regions with different physical properties exhibits distinctive characteristics, differing from both the homogeneous case and the heterogeneous cases where the well does not traverse distinct regions. Permeability heterogeneity influences the curves of all other flow regimes, except the early and late flow regimes. Faults affect transient pressure behavior only when not positioned in the middle of each two primary fractures. Region area heterogeneity primarily influences the medium flow regimes. This work provides valuable insights into the performance of MFHWs in channelized heterogeneous reservoirs, offering technical support for well testing in these reservoirs.
Item
Open Access
Performance of multistage-fractured horizontal wells with secondary discrete fractures in heterogeneous tight reservoirs
(2024-02-13) Deng, Qi; Qu, Jianhua; Mi, Zhongrong; Xu, Bing; Lv, Xindong; Huang, Kai; Zhang, Boning; Nie, Ren-Shi; Chen, Shengnan
Abstract A significant portion of tight sandstone reservoirs commonly displays intricate fluvial channels or fault systems. Despite various attempts at analytical/semi-analytical modeling of multistage-fractured horizontal wells (MFHWs) in unconventional reservoirs, the majority of studies have focused on scenarios with homogeneous original physical properties, neglecting cases where MFHWs traverse multiple regions in channelized heterogeneous reservoirs. Comprehending the influence of heterogeneous and leaky faults on the performance of MFHWs is essential for efficient development. This study presents an innovative semi-analytical model to analyze the pressure transient behavior of MFHWs with secondary fractures as they traverse multiple regions in banded channel heterogeneous reservoirs, particularly considering the presence of partially-communicating faults. The approach combines the source method and Green’s function method to obtain solutions, introducing a novel technique for discretizing fractures without discretizing interfaces. The effects of the reservoir heterogeneity, partially-communicating faults and fractures system on pressure behavior are analyzed. The results indicate that the pressure behavior of MFHWs passing through regions with different physical properties exhibits distinctive characteristics, differing from both the homogeneous case and the heterogeneous cases where the well does not traverse distinct regions. Permeability heterogeneity influences the curves of all other flow regimes, except the early and late flow regimes. Faults affect transient pressure behavior only when not positioned in the middle of each two primary fractures. Region area heterogeneity primarily influences the medium flow regimes. This work provides valuable insights into the performance of MFHWs in channelized heterogeneous reservoirs, offering technical support for well testing in these reservoirs.
Item
Open Access
Evaluating the coding accuracy of type 2 diabetes mellitus among patients with non-alcoholic fatty liver disease
(2024-02-16) Lee, Seungwon; Shaheen, Abdel A.; Campbell, David J. T.; Naugler, Christopher; Jiang, Jason; Walker, Robin L.; Quan, Hude; Lee, Joon
Abstract Background Non-alcoholic fatty liver disease (NAFLD) describes a spectrum of chronic fattening of liver that can lead to fibrosis and cirrhosis. Diabetes has been identified as a major comorbidity that contributes to NAFLD progression. Health systems around the world make use of administrative data to conduct population-based prevalence studies. To that end, we sought to assess the accuracy of diabetes International Classification of Diseases (ICD) coding in administrative databases among a cohort of confirmed NAFLD patients in Calgary, Alberta, Canada. Methods The Calgary NAFLD Pathway Database was linked to the following databases: Physician Claims, Discharge Abstract Database, National Ambulatory Care Reporting System, Pharmaceutical Information Network database, Laboratory, and Electronic Medical Records. Hemoglobin A1c and diabetes medication details were used to classify diabetes groups into absent, prediabetes, meeting glycemic targets, and not meeting glycemic targets. The performance of ICD codes among these groups was compared to this standard. Within each group, the total numbers of true positives, false positives, false negatives, and true negatives were calculated. Descriptive statistics and bivariate analysis were conducted on identified covariates, including demographics and types of interacted physicians. Results A total of 12,012 NAFLD patients were registered through the Calgary NAFLD Pathway Database and 100% were successfully linked to the administrative databases. Overall, diabetes coding showed a sensitivity of 0.81 and a positive predictive value of 0.87. False negative rates in the absent and not meeting glycemic control groups were 4.5% and 6.4%, respectively, whereas the meeting glycemic control group had a 42.2% coding error. Visits to primary and outpatient services were associated with most encounters. Conclusion Diabetes ICD coding in administrative databases can accurately detect true diabetic cases. However, patients with diabetes who meets glycemic control targets are less likely to be coded in administrative databases. A detailed understanding of the clinical context will require additional data linkage from primary care settings.