Context-Aware Access Control Model for Cloud Computing

In view of malicious insider attacks on cloud computing environments, a new Context-Aware Access Control Model for cloud computing (CAACM) was presented. According to the characteristic of cloud computing, we take spatial state, temporal state and platform trust level as context. The model establishes mechanisms of authorization from cloud management role to objects, which enables dynamic activation of role permission by associating cloud management role with context. It also achieves fine-grained access control on cloud objects by supervising the permission of management role in full life cycle. Moreover, it introduces the concept of exclusive managerial role, which extends access control from static protection on resources to dynamic authorization on managerial roles. Further, it describes the approach of role permission activation systematically. CAACM formally proves to be safe and it lays the groundwork for the deployment of CAACM in cloud computing systems

Research on Methods for Discovering and Selecting Cloud Infrastructure Services Based on Feature Modeling

Nowadays more and more cloud infrastructure service providers are providing large numbers of service instances which are a combination of diversified resources, such as computing, storage, and network. However, for cloud infrastructure services, the lack of a description standard and the inadequate research of systematic discovery and selection methods have exposed difficulties in discovering and choosing services for users. First, considering the highly configurable properties of a cloud infrastructure service, the feature model method is used to describe such a service. Second, based on the description of the cloud infrastructure service, a systematic discovery and selection method for cloud infrastructure services are proposed. The automatic analysis techniques of the feature model are introduced to verify the model’s validity and to perform the matching of the service and demand models. Finally, we determine the critical decision metrics and their corresponding measurement methods for cloud infrastructure services, where the subjective and objective weighting results are combined to determine the weights of the decision metrics. The best matching instances from various providers are then ranked by their comprehensive evaluations. Experimental results show that the proposed methods can effectively improve the accuracy and efficiency of cloud infrastructure service discovery and selection

Study on imbibition during the CO2 enhanced oil recovery in fractured tight sandstone reservoirs

CO2 enhanced oil recovery (CO2-EOR) is a key technology for improving the oil recovery of fractured tight reservoirs, and imbibition has been recognized as an important mechanism for oil recovery in low-permeability reservoirs. To clarify the imbibition role and influencing factors during the CO2-EOR process in fractured tight oil reservoirs and also improve the EOR mechanism, a high-temperature and high-pressure CO2 imbibition experiment was performed based on the nuclear magnetic resonance technology. The results show that high pressure and high permeability are beneficial to imbibition efficiency. The salinity of the imbibition fluid is not very sensitive to the imbibition recovery. In addition, the CO2 increases the imbibition speed and can also significantly improve the production rate and oil recovery. It is beneficial to increase the CO2 concentration to shorten the imbibition equilibrium time and enhance oil recovery. According to the results of the nuclear magnetic resonance study, although the nanopore can provide a greater imbibition force, the oil flow resistance is also larger, but CO2 can reduce the flow resistance of oil and be conducive to oil production in smaller pores. The inclusion of imbibition into the research category of CO2-EOR mechanism will be more in line with field practice and more scientific in fractured tight reservoirs, thus providing theoretical support for the development and improvement of the CO2-EOR technology.Document Type: Original articleCited as: Wang, Y., Shang, Q., Guo, J., Zhou, L. Study on imbibition during the CO2 enhanced oil recovery in fractured tight sandstone reservoirs. Capillarity, 2023, 7(3): 47-56. https://doi.org/10.46690/capi.2023.06.0

Nanoporous Structure of Sintered Metal Powder Heat Exchanger in Dilution Refrigeration: A Numerical Study

We use LAMMPS to randomly pack hard spheres to simulate the heat exchanger, where the hard spheres represent sintered metal particles in the heat exchanger. We simulated the heat exchanger under different sphere radii and different packing fractions of the metal particle and researched pore space. To improve the performance of the heat exchanger, we adopted this simulation method to explore when the packing fraction is 65%, the optimal sintering particle radius in the heat exchanger is 30~35nm.Comment: 5 pages,3 figures, one tabl

A Reputation-Based Identity Management Model for Cloud Computing

In the field of cloud computing, most research on identity management has concentrated on protecting user data. However, users typically leave a trail when they access cloud services, and the resulting user traceability can potentially lead to the leakage of sensitive user information. Meanwhile, malicious users can do harm to cloud providers through the use of pseudonyms. To solve these problems, we introduce a reputation mechanism and design a reputation-based identity management model for cloud computing. In the model, pseudonyms are generated based on a reputation signature so as to guarantee the untraceability of pseudonyms, and a mechanism that calculates user reputation is proposed, which helps cloud service providers to identify malicious users. Analysis verifies that the model can ensure that users access cloud services anonymously and that cloud providers assess the credibility of users effectively without violating user privacy

A Feasibility Study of the Integration of Enhanced Oil Recovery (CO2 Flooding) with CO2 Storage in the Mature Oil Fields of the Ordos Basin, China

AbstractRich in energy resources, China's Ordos Basin Shares many similarities with Wyoming's Powder River Basin. As a result, the experience and expertise pertaining to energy development in the Powder River Basin should prove helpful in the Ordos Basin. The b reserves are ranked fourth. The coal deposits in the Ordos Basin account for 39 percent of total Chinese coal reserves (3.98 trillion tonnes), and six of the thirteen largest coal mines in China are located in the basin. The overlapping development of relatively new coal conversion industries with existing oil and gas industries in northern Shaanxi Province is creating an opportunity to apply the systematic approach developed in Wyoming: the integration of geological CO2 storage and CO2-EOR. The coal conversion industry (i.e., coal-to-methanol, coal-to-olefins, etc.) provides affordable, capture-ready CO2 sources for developing large-scale integrated CO2-EOR and carbon storage projects in the Ordos Basin, China. Compared with other CCUS projects, the ability to use CO2 from the coal- conversion industry for CO2-EOR and subsequent geological CO2 storage will make integrated projects in the Ordos Basin more cost-effective and technologically efficient.The low porosity, low permeability, low oil saturation, anomalously low reservoir pressure, and high reservoir heterogeneity of the target storage formations in the Ordos Basin make using CO2 for enhanced oil recovery much more challenging here than in the US. These reservoir characteristics together constitute a major reason that CO2- EOR is not widely employed in the Ordos Basin, even though sources of highly concentrated CO2 (coal conversion plants) have been available for years. Comparisons of reservoir and crude oil properties in the Ordos Basin with the current US CO2-EOR screening guidelines reveal that gravity, viscosity, crude oil composition, and formation type of the Ordos reservoirs all are favorable for CO2 miscible flooding. The major challenges in deploying EOR result from anomalously low reservoir pressure, low porosity, and higher reservoir heterogeneity

Preparation and Characteristic of PC/PLA/TPU Blends by Reactive Extrusion

To overcome the poor toughness of PC/PLA blends due to the intrinsic properties of materials and poor compatibility, thermoplastic urethane (TPU) was added to PC/PLA blends as a toughener; meantime, catalyst di-n-butyltin oxide (DBTO) was also added for catalyzing transesterification of components in order to modify the compatibility of blends. The mechanical, thermal, and rheological properties of blends were investigated systematically. The results showed that the addition of TPU improves the toughness of PC/PLA blends significantly, with the increase of TPU, the elongation at break increases considerably, and the impact strength increases firstly and then falls, while the tensile strength decreases significantly and the blends exhibit a typical plastic fracture behavior. Meantime, TPU is conducive to the crystallinity of PLA in blends which is inhibited seriously by PC and damages the thermal stability of blends slightly. Moreover, the increased TPU makes the apparent viscosity of blends melt decrease due to the well melt fluidity of TPU; the melt is closer to the pseudoplasticity melt. Remarkably, the transesterification between the components improves the compatibility of blends significantly, and more uniform structure results in a higher crystallinity and better mechanical properties

A Reputation-Based Identity Management Model for Cloud Computing

In the field of cloud computing, most research on identity management has concentrated on protecting user data. However, users typically leave a trail when they access cloud services, and the resulting user traceability can potentially lead to the leakage of sensitive user information. Meanwhile, malicious users can do harm to cloud providers through the use of pseudonyms. To solve these problems, we introduce a reputation mechanism and design a reputation-based identity management model for cloud computing. In the model, pseudonyms are generated based on a reputation signature so as to guarantee the untraceability of pseudonyms, and a mechanism that calculates user reputation is proposed, which helps cloud service providers to identify malicious users. Analysis verifies that the model can ensure that users access cloud services anonymously and that cloud providers assess the credibility of users effectively without violating user privacy

Influencing factors of micropores in the graptolite shale of Ordovician Pingliang Formation in Ordos Basin, NW China

Multiple tests were conducted on graptolite shale samples from Middle Ordovician Pingliang Formation in three typical areas in Ordos Basin to investigate the relationship between micro-nano pore structure, graptolite content, rock composition, TOC, maturity, main and trace elements and gas content. The graptolite of Pingliang Formation concentrates in the black shale at the lower section of this layer. Pores in the shale are diverse in types, including pores made by extracellular polymeric substance (EPS), in bio-graptolite body, as inter-granular void of clay minerals, intra-granular, interstitial space between mineral crystals, micro-fractures, and intra-granular dissolution structures etc. Tests show that graptolite affected the sedimentary environment and shale gas accumulation; graptolites content is positively correlated to TOC, in a certain range, specific surface area is positively correlated to TOC and maturity, etc., as overall a lithologic inorganic and organic ratios. The rare earth elements (REE) patterns of the three areas are similar, indicating the same provenance. REE, Fe, Al and Ti content are negatively correlated to TOC, indicating the high REE content is not caused by organic matter enrichment, but related to the absorption of minerals particles. Gas content is positively correlated to specific surface area, TOC and maturity. The above factors contribute to space and size distribution of micro-nano pores in shale. Key words: graptolite shale, pore type, geochemical parameters, Ordovician Pingliang Formation, Ordos Basi