17,386 research outputs found
Stochastic Tools for Network Intrusion Detection
With the rapid development of Internet and the sharp increase of network
crime, network security has become very important and received a lot of
attention. We model security issues as stochastic systems. This allows us to
find weaknesses in existing security systems and propose new solutions.
Exploring the vulnerabilities of existing security tools can prevent
cyber-attacks from taking advantages of the system weaknesses. We propose a
hybrid network security scheme including intrusion detection systems (IDSs) and
honeypots scattered throughout the network. This combines the advantages of two
security technologies. A honeypot is an activity-based network security system,
which could be the logical supplement of the passive detection policies used by
IDSs. This integration forces us to balance security performance versus cost by
scheduling device activities for the proposed system. By formulating the
scheduling problem as a decentralized partially observable Markov decision
process (DEC-POMDP), decisions are made in a distributed manner at each device
without requiring centralized control. The partially observable Markov decision
process (POMDP) is a useful choice for controlling stochastic systems. As a
combination of two Markov models, POMDPs combine the strength of hidden Markov
Model (HMM) (capturing dynamics that depend on unobserved states) and that of
Markov decision process (MDP) (taking the decision aspect into account).
Decision making under uncertainty is used in many parts of business and
science.We use here for security tools.We adopt a high-quality approximation
solution for finite-space POMDPs with the average cost criterion, and their
extension to DEC-POMDPs. We show how this tool could be used to design a
network security framework.Comment: Accepted by International Symposium on Sensor Networks, Systems and
Security (2017
Statistical physics of isotropic-genesis nematic elastomers: I. Structure and correlations at high temperatures
Isotropic-genesis nematic elastomers (IGNEs) are liquid crystalline polymers
(LCPs) that have been randomly, permanently cross-linked in the
high-temperature state so as to form an equilibrium random solid. Thus, instead
of being free to diffuse throughout the entire volume, as they would be in the
liquid state, the constituent LCPs in an IGNE are mobile only over a finite
length-scale controlled by the density of cross-links. We address the effects
that such network-induced localization have on the liquid-crystalline
characteristics of an IGNE, as probed via measurements made at high
temperatures. In contrast with the case of uncross-linked LCPs, for IGNEs these
characteristics are determined not only by thermal fluctuations but also by the
quenched disorder associated with the cross-link constraints. To study IGNEs,
we consider a microscopic model of dimer nematogens in which the dimers
interact via orientation-dependent excluded volume forces. The dimers are,
furthermore, randomly, permanently cross-linked via short Hookean springs, the
statistics of which we model by means of a Deam-Edwards type of distribution.
We show that at length-scales larger than the size of the nematogens this
approach leads to a recently proposed phenomenological Landau theory of IGNEs
[Lu et al., Phys. Rev. Lett. 108, 257803 (2012)], and hence predicts a regime
of short-ranged oscillatory spatial correlations in the nematic alignment, of
both thermal and glassy types. In addition, we consider two alternative
microscopic models of IGNEs: (i) a wormlike chain model of IGNEs that are
formed via the cross-linking of side-chain LCPs; and (ii) a jointed chain model
of IGNEs that are formed via the cross-linking of main-chain LCPs. At large
length-scales, both of these models give rise to liquid-crystalline
characteristics that are qualitatively in line with those predicted by the
dimer-and-springs model.Comment: 33 pages, 6 figures, 6 appendice
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Enhancing microRNA167A expression in seed decreases the α-linolenic acid content and increases seed size in Camelina sativa.
Despite well established roles of microRNAs in plant development, few aspects have been addressed to understand their effects in seeds especially on lipid metabolism. In this study, we showed that overexpressing microRNA167A (miR167OE) in camelina (Camelina sativa) under a seed-specific promoter changed fatty acid composition and increased seed size. Specifically, the miR167OE seeds had a lower α-linolenic acid with a concomitantly higher linoleic acid content than the wild-type. This decreased level of fatty acid desaturation corresponded to a decreased transcriptional expression of the camelina fatty acid desaturase3 (CsFAD3) in developing seeds. MiR167 targeted the transcription factor auxin response factor (CsARF8) in camelina, as had been reported previously in Arabidopsis. Chromatin immunoprecipitation experiments combined with transcriptome analysis indicated that CsARF8 bound to promoters of camelina bZIP67 and ABI3 genes. These transcription factors directly or through the ABI3-bZIP12 pathway regulate CsFAD3 expression and affect α-linolenic acid accumulation. In addition, to decipher the miR167A-CsARF8 mediated transcriptional cascade for CsFAD3 suppression, transcriptome analysis was conducted to implicate mechanisms that regulate seed size in camelina. Expression levels of many genes were altered in miR167OE, including orthologs that have previously been identified to affect seed size in other plants. Most notably, genes for seed coat development such as suberin and lignin biosynthesis were down-regulated. This study provides valuable insights into the regulatory mechanism of fatty acid metabolism and seed size determination, and suggests possible approaches to improve these important traits in camelina
Making an impact: The influence of policies to reduce emissions from aviation on the business travel patterns of individual corporations
The contribution of aviation to global carbon dioxide (CO2) emissions is projected to triple by 2050. As nations strive to meet CO2 reduction targets, policy interventions to manage the growth of emissions arising from air travel are likely. Here, we investigate the potential influence of aviation emissions reduction policies on the business travel patterns of individual corporations. Using travel data from six UK-based companies, we find that increased ticket prices can deliver substantial emissions cuts, particularly on premium class flights, and may provide strong financial incentives to seek modal and/or technological alternatives to flying. We also find that corporations from different business sectors vary in their responsiveness to arange of policy options. Finally, we examine questionnaire data to determine whether companies more broadly are going beyond compliance to mitigate their environmental impact by managing travel-related emissions voluntarily. Although many corporations are measuring and reporting emissions, only a limited number are willing to implement in-house reduction policies prior to regulation
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