5,427 research outputs found
Direct Acyclic Graph based Ledger for Internet of Things: Performance and Security Analysis
Direct Acyclic Graph (DAG)-based ledger and the corresponding consensus
algorithm has been identified as a promising technology for Internet of Things
(IoT). Compared with Proof-of-Work (PoW) and Proof-of-Stake (PoS) that have
been widely used in blockchain, the consensus mechanism designed on DAG
structure (simply called as DAG consensus) can overcome some shortcomings such
as high resource consumption, high transaction fee, low transaction throughput
and long confirmation delay. However, the theoretic analysis on the DAG
consensus is an untapped venue to be explored. To this end, based on one of the
most typical DAG consensuses, Tangle, we investigate the impact of network load
on the performance and security of the DAG-based ledger. Considering unsteady
network load, we first propose a Markov chain model to capture the behavior of
DAG consensus process under dynamic load conditions. The key performance
metrics, i.e., cumulative weight and confirmation delay are analysed based on
the proposed model. Then, we leverage a stochastic model to analyse the
probability of a successful double-spending attack in different network load
regimes. The results can provide an insightful understanding of DAG consensus
process, e.g., how the network load affects the confirmation delay and the
probability of a successful attack. Meanwhile, we also demonstrate the
trade-off between security level and confirmation delay, which can act as a
guidance for practical deployment of DAG-based ledgers.Comment: accepted by IEEE Transactions on Networkin
Phylogenetic and evolutionary analysis of the septin protein family in metazoan
AbstractSeptins, a conserved family of cytoskeletal GTP-binding proteins, were presented in diverse eukaryotes. Here, a comprehensive phylogenetic and evolutionary analysis for septin proteins in metazoan was carried out. First, we demonstrated that all septin proteins in metazoan could be clustered into four subgroups, and the representative homologue of every subgroup was presented in the non-vertebrate chordate Ciona intestinalis, indicating that the emergence of the four septin subgroups should have occurred prior to divergence of vertebrates and invertebrates, and the expansion of the septin gene number in vertebrates was mainly by the duplication of pre-existing genes rather than by the appearance of new septin subgroup. Second, the direct orthologues of most human septins existed in zebrafish, which suggested that human septin gene repertoire was mainly formed by as far as before the split between fishes and land vertebrates. Third, we found that the evolutionary rate within septin family in mammalian lineage varies significantly, human SEPT1, SEPT 10, SEPT 12, and SEPT 14 displayed a relative elevated evolutionary rate compared with other septin members. Our data will provide new insights for the further function study of this protein family
The evolution of BIR domain and its containing proteins
AbstractBIR domain and its containing proteins play critical roles in cell apoptosis and cell division. Here several lines of novelty were revealed based on a comprehensive evolutionary analysis of BIR domains in 11 representative organisms. First, the type II BIR domains in Survivin and Bruce showed more conservation compared with the type I BIR domains in the inhibitors of apoptosis proteins (IAPs). Second, cIAP was derived from a XIAP duplicate and emerged just after the divergence of invertebrates and vertebrates. Third, the three BIR domains of NAIP displayed significantly elevated evolutionary rates compared with the BIR domains in other IAPs
The instability of the inner horizon of the quantum-corrected black hole
We analyse the stability of the inner horizon of the quantum-corrected black
hole which is proposed in loop quantum gravity as the exterior of the quantum
Oppenheimer-Snyder and Swiss Cheese models. It is shown that the flux and
energy density of a test scalar field measured by free-falling observers are
both divergent near the Cauchy horizon. By considering the generalized Dray-'t
Hooft-Redmond relation which is independent of the field equation, we find that
the mass inflation always happens and the scalar curvature and Kretschmann
scalar are also divergent on the inner horizon. These suggest that the inner
horizon is unstable and will probably turn into a null singularity. The results
support the strong cosmic censorship hypothesis. However, this also implies
that the quantum corrected model may not be the definitive endpoint as a
regular black hole. Besides, it further proposes that any possible observable
astronomical phenomenon which depends on the existence of the inner horizon of
the black hole is not reliable.Comment: 12 pages, 1 figur
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