COMPARS: Toward an empirical approach for comparing the resilience of reputation systems

Reputation is a primary mechanism for trust management in decentralized systems. Many reputation-based trust functions have been proposed in the literature. However, picking the right trust function for a given decentralized system is a non-trivial task. One has to consider and balance a variety of factors, including computation and communication costs, scalability and resilience to manipulations by attackers. Although the former two are relatively easy to evaluate, the evaluation of resilience of trust functions is challenging. Most existing work bases evaluation on static attack models, which is unrealistic as it fails to reflect the adaptive nature of adversaries (who are often real human users rather than simple computing agents). In this paper, we highlight the importance of the modeling of adaptive attackers when evaluating reputation-based trust functions, and propose an adaptive framework-called COMPARS-for the evaluation of resilience of reputation systems. Given the complexity of reputation systems, it is often difficult, if not impossible, to exactly derive the optimal strategy of an attacker. Therefore, COMPARS takes a practical approach that attempts to capture the reasoning process of an attacker as it decides its next action in a reputation system. Specifically, given a trust function and an attack goal, COMPARS generates an attack tree to estimate the possible outcomes of an attacker's action sequences up to certain points in the future. Through attack trees, COMPARS simulates the optimal attack strategy for a specific reputation function f, which will be used to evaluate the resilience of f. By doing so, COMPARS allows one to conduct a fair and consistent comparison of different reputation functions. Copyright 2014 ACM.Reputation is a primary mechanism for trust management in decentralized systems. Many reputation-based trust functions have been proposed in the literature. However, picking the right trust function for a given decentralized system is a non-trivial task. One has to consider and balance a variety of factors, including computation and communication costs, scalability and resilience to manipulations by attackers. Although the former two are relatively easy to evaluate, the evaluation of resilience of trust functions is challenging. Most existing work bases evaluation on static attack models, which is unrealistic as it fails to reflect the adaptive nature of adversaries (who are often real human users rather than simple computing agents). In this paper, we highlight the importance of the modeling of adaptive attackers when evaluating reputation-based trust functions, and propose an adaptive framework-called COMPARS-for the evaluation of resilience of reputation systems. Given the complexity of reputation systems, it is often difficult, if not impossible, to exactly derive the optimal strategy of an attacker. Therefore, COMPARS takes a practical approach that attempts to capture the reasoning process of an attacker as it decides its next action in a reputation system. Specifically, given a trust function and an attack goal, COMPARS generates an attack tree to estimate the possible outcomes of an attacker's action sequences up to certain points in the future. Through attack trees, COMPARS simulates the optimal attack strategy for a specific reputation function f, which will be used to evaluate the resilience of f. By doing so, COMPARS allows one to conduct a fair and consistent comparison of different reputation functions. Copyright 2014 ACM

Characterization of Trichococcus paludicola sp nov and Trichococcus alkaliphilus sp nov., isolated from a high-elevation wetland, by phenotypic and genomic analyses

Two psychrotolerant facultative anaerobes, strains B7-2(T) and B5(T), were isolated from the Zoige Wetland on the Qinghai-Tibetan Plateau. The 16S rRNA gene sequences of strains B7-2(T) and B5(T) shared high similarity (>99?%) with those of the type strains of the genus Trichococcus, while their digital DNADNA hybridization values with each other (49?%) and with the reference type strains (4823?%) were lower than 70?%, which suggest that they represent two novel species of the genus Trichococcus. Cells of strains B7-2(T) and B5(T) were immotile cocci, grew in the temperature range of 437 degrees C (optimum 25 degrees C) and were alkaliphilic with optimum growth at pH 9.0. The major components of the cellular fatty acids were C-16:0, anteiso-C-17:0 and C-18:0 for strain B7-2(T), and C-16:0, anteiso-C-17:0, C-18:1 omega 9c and C-18:0 for strain B5(T). The genomic DNA G+C contents were 46.0 and 46.7 mol% for strains B7-2(T) and B5(T), respectively. Based on physiological and genomic characteristics, it is suggested that strains B7-2(T) and B5(T) represent two novel species within the genus Trichococcus, for which the names Trichococcus paludicola sp. nov. and Trichococcus alkaliphilus sp. nov. are proposed. The type strains are B7-2(T) (=DSM 104691T=KCTC 33886(T)) and B5(T) (=DSM 104692(T)=KCTC 33885(T)), respectively

Anti-apoptotic and mitochondrial biogenetic Effects of Exercise Training on Ovariectomized Hypertensive Rats heart

[[abstract]]This study was to investigate the effects of exercise training on antiapoptotic pathways and mitochondrial biogenesis in ovariectomized hypertensive rats. Histopathological analysis, TUNEL assay, and Western blotting were performed on the excised hearts from female spontaneously hypertensive rats (SHR), which were divided into a sham-operated sedentary hypertensive (SHR-S), a sedentary hypertensive ovariectomized (SHR-O), and hypertensive ovariectomized rats that underwent treadmill exercise training (SHR-OT; 60 min/day, 5 days/wk) for 8 wk, along with normotensive Wistar Kyoto rats (WKY). When compared with the WKY group, the SHR-S group exhibited decreased protein levels of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and mitochondrial OPA-1 (mitochondrial biogenesis) and decreased further in the SHR-O group. The protein levels of p-PI3K, p-Akt, Bcl-2, Bcl-xL (prosurvival pathways), and the protein levels of PGC-1α and mitochondrial OPA1 (mitochondrial biogenesis) were increased in the SHR-OT group, but estrogen receptor (ER)α and ERβ were not changed when compared with the SHR-O group. The protein levels of t-Bid, Bad, Bax, cytosolic cytochrome c, activated caspase 9, and activated caspase 3 (mitochondria-dependent apoptotic pathways), as well as Fas ligand, TNF-α, Fas receptors, Fas-associated death domain, activated caspase 8 (Fas receptor-dependent apoptotic pathways) were decreased in the SHR-OT group, when compared with the SHR-O group. Exercise training protection on the coexistence of hypertension and ovariectomy-induced cardiac mitochondria-dependent and Fas receptor-dependent apoptotic pathways by enhancing the Bcl2-related and mitochondrial biogenetic prosurvival pathways might provide a new therapeutic effect on cardiac protection in oophorectomized early postmenopausal hypertensive women. NEW & NOTEWORTHY Widely dispersed cardiac apoptosis was found in the coexistence of hypertension and ovariectomy. Exercise training on a treadmill could prevent ovariectomized hypertension-induced widely dispersed cardiac apoptosis via mitochondria-dependent apoptotic pathway (t-Bid, Bad, Bax, cytosolic cytochrome c, activated caspase 9, and activated caspase 3) and Fas receptor-dependent apoptotic pathway (Fas ligand, tumor necrosis factor-α, Fas receptors, Fas-associated death domain, activated caspase 8, and activated caspase 3) through enhancing the Bcl2-related (p-PI3K, p-Akt, Bcl-2, Bcl-xL) and mitochondrial biogenetic (PGC-1α and mitochondrial optic atrophy 1) prosurvival pathways