252,276 research outputs found
Coding against a Limited-view Adversary: The Effect of Causality and Feedback
We consider the problem of communication over a multi-path network in the
presence of a causal adversary. The limited-view causal adversary is able to
eavesdrop on a subset of links and also jam on a potentially overlapping subset
of links based on the current and past information. To ensure that the
communication takes place reliably and secretly, resilient network codes with
necessary redundancy are needed. We study two adversarial models - additive and
overwrite jamming and we optionally assume passive feedback from decoder to
encoder, i.e., the encoder sees everything that the decoder sees. The problem
assumes transmissions are in the large alphabet regime. For both jamming
models, we find the capacity under four scenarios - reliability without
feedback, reliability and secrecy without feedback, reliability with passive
feedback, reliability and secrecy with passive feedback. We observe that, in
comparison to the non-causal setting, the capacity with a causal adversary is
strictly increased for a wide variety of parameter settings and present our
intuition through several examples.Comment: 15 page
What Makes Autocraciesâ Soft Power Strategies Special? Evidence from Russia and China
The paper problematizes the national soft power strategies of authoritarian states
arguing that many of their features stem from those countriesâ political regime. In
particular, the author focuses on such features as actors involved in soft power
policies, the public mediaâs international and domestic rhetoric, the presence or
absence of ideological commitments, strategiesâ proactiveness/reactiveness as
well as their long- and short-termness. The author presents his argumentation in
a fashion similar to what is called theory-building process tracing: first, he shows
causal links between an autocratic political regime and each of those features, and
then illustrates them with relevant examples taken from case studies and media
publications on the soft power strategies of contemporary Russia and China
Extracting causation from millennial-scale climate fluctuations in the last 800 kyr
The detection of cause-effect relationships from the analysis of
paleoclimatic records is a crucial step to disentangle the main mechanisms at
work in the climate system. Here, we show that the approach based on the
generalized Fluctuation-Dissipation Relation, complemented by the analysis of
the Transfer Entropy, allows the causal links to be identified between
temperature, CO2 concentration and astronomical forcing during the glacial
cycles of the last 800 kyr based on Antarctic ice core records. When
considering the whole spectrum of time scales, the results of the analysis
suggest that temperature drives CO2 concentration, or that are both driven by
the common astronomical forcing. However, considering only millennial-scale
fluctuations, the results reveal the presence of more complex causal links,
indicating that CO2 variations contribute to driving the changes of temperature
on such time scales. The results also evidence a slow temporal variability in
the strength of the millennial-scale causal links between temperature and CO2
concentration.Comment: 13 pages, 5 figures + Supplemental material (10 pages, 7 figures
A CAUSAL ANALYSIS OF THE DEFENCE-GROWTH RELATIONSHIPS: EVIDENCE FROM THE BALKANS
The causal relationships between military burden and economic growth have attracted considerable interest of academics, scholars and practitioners during the last three decades. This survey is hoping to contribute to the existing pool of literature by investigating the causal links between defence spending and economic growth for three developing Balkan countries (Bulgaria, Romania and Albania) and their mature counterpart in the Balkan Peninsula (Greece) during the period 1988-2009. Empirical results imply that there are no bilateral links between the tested variables for any of the tested countries. However, findings indicate the presence of one-way causal links running from military expenditures to GDP only for Bulgaria and Albania, implying the significant impact of defence burden on growth for these countries. On the other hand, empirical results for Greece and Romania suggest that defence spending and GDP growth are independent, which favours neutrality hypothesis. Nevertheless, it should be mentioned that we would expect to find significant links especially in the case of Greece, due to the fact that the country presents the highest defence expenditures in the Balkan region for the last fifteen years. These contradictory results could be due to different levels of maturity between the tested countries but it could also be attributed to temporary changes of accounting practises (i.e. recording expenses when military material was ordered rather than received, as evidenced in the case of Greece in the late 1990âs by government officials). These accounting changes could be the obstacle in some cases (e.g. Greece) to provide empirical evidence of the links between defence burden and economic growth
Responding to global challenges in food, energy, environment and water: Risks and options assessment for decision-Making
We analyse the threats of global environmental change, as they relate to food security. First, we review three discourses: (i) âsustainable intensificationâ, or the increase of food supplies without compromising food producing inputs, such as soils and water; (ii) the ânexusâ that seeks to understand links across food, energy, environment and water systems; and (iii) âresilience thinkingâ that focuses on how to ensure the critical capacities of food, energy and water systems are maintained in the presence of uncertainties and threats. Second, we build on these discourses to present the causal, risks and options assessment for decision-making process to improve decision-making in the presence of risks. The process provides a structured, but flexible, approach that moves from problem diagnosis to better risk-based decision-making and outcomes by responding to causal risks within and across food, energy, environment and water systems
Understanding causation via correlations and linear response theory
In spite of the (correct) common-wisdom statement correlation does not imply
causation, a proper employ of time correlations and of fluctuation-response
theory allows to understand the causal relations between the variables of a
multi-dimensional linear Markov process. It is shown that the
fluctuation-response formalism can be used both to find the direct causal links
between the variables of a system and to introduce a degree of causation,
cumulative in time, whose physical interpretation is straightforward. Although
for generic non-linear dynamics there is no simple exact relationship between
correlations and response functions, the described protocol can still give a
useful proxy also in presence of weak nonlinear terms
Synergy and redundancy in the Granger causal analysis of dynamical networks
We analyze by means of Granger causality the effect of synergy and redundancy
in the inference (from time series data) of the information flow between
subsystems of a complex network. Whilst we show that fully conditioned Granger
causality is not affected by synergy, the pairwise analysis fails to put in
evidence synergetic effects.
In cases when the number of samples is low, thus making the fully conditioned
approach unfeasible, we show that partially conditioned Granger causality is an
effective approach if the set of conditioning variables is properly chosen. We
consider here two different strategies (based either on informational content
for the candidate driver or on selecting the variables with highest pairwise
influences) for partially conditioned Granger causality and show that depending
on the data structure either one or the other might be valid. On the other
hand, we observe that fully conditioned approaches do not work well in presence
of redundancy, thus suggesting the strategy of separating the pairwise links in
two subsets: those corresponding to indirect connections of the fully
conditioned Granger causality (which should thus be excluded) and links that
can be ascribed to redundancy effects and, together with the results from the
fully connected approach, provide a better description of the causality pattern
in presence of redundancy. We finally apply these methods to two different real
datasets. First, analyzing electrophysiological data from an epileptic brain,
we show that synergetic effects are dominant just before seizure occurrences.
Second, our analysis applied to gene expression time series from HeLa culture
shows that the underlying regulatory networks are characterized by both
redundancy and synergy
Beyond Covariation: Cues to Causal Structure
Causal induction has two components: learning about the structure of causal models and learning about causal strength and other quantitative parameters. This chapter argues for several interconnected theses. First, people represent causal knowledge qualitatively, in terms of causal structure; quantitative knowledge is derivative. Second, people use a variety of cues to infer causal structure aside from statistical data (e.g. temporal order, intervention, coherence with prior knowledge). Third, once a structural model is hypothesized, subsequent statistical data are used to confirm, refute, or elaborate the model. Fourth, people are limited in the number and complexity of causal models that they can hold in mind to test, but they can separately learn and then integrate simple models, and revise models by adding and removing single links. Finally, current computational models of learning need further development before they can be applied to human learning
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