6,239 research outputs found
Modelling Concurrency with Comtraces and Generalized Comtraces
Comtraces (combined traces) are extensions of Mazurkiewicz traces that can
model the "not later than" relationship. In this paper, we first introduce the
novel notion of generalized comtraces, extensions of comtraces that can
additionally model the "non-simultaneously" relationship. Then we study some
basic algebraic properties and canonical reprentations of comtraces and
generalized comtraces. Finally we analyze the relationship between generalized
comtraces and generalized stratified order structures. The major technical
contribution of this paper is a proof showing that generalized comtraces can be
represented by generalized stratified order structures.Comment: 49 page
Revisiting bisimilarity and its modal logic for nondeterministic and probabilistic processes
We consider PML, the probabilistic version of Hennessy-Milner logic introduced by Larsen and Skou to characterize bisimilarity over probabilistic processes without internal
nondeterminism.We provide two different interpretations for PML by considering nondeterministic and probabilistic processes as models, and we exhibit two new bisimulation-based equivalences that are in full agreement with those interpretations. Our new equivalences include
as coarsest congruences the two bisimilarities for nondeterministic and probabilistic processes proposed by Segala and Lynch. The latter equivalences are instead in agreement with two versions of Hennessy-Milner logic extended with an additional probabilistic operator
interpreted over state distributions rather than over individual states. Thus, our new interpretations of PML and the corresponding new bisimilarities offer a uniform framework for reasoning on processes that are purely nondeterministic or reactive probabilistic or are mixing nondeterminism and probability in an alternating/non-alternating way
Analyzing the Digital Traces of Political Manipulation: The 2016 Russian Interference Twitter Campaign
Until recently, social media was seen to promote democratic discourse on
social and political issues. However, this powerful communication platform has
come under scrutiny for allowing hostile actors to exploit online discussions
in an attempt to manipulate public opinion. A case in point is the ongoing U.S.
Congress' investigation of Russian interference in the 2016 U.S. election
campaign, with Russia accused of using trolls (malicious accounts created to
manipulate) and bots to spread misinformation and politically biased
information. In this study, we explore the effects of this manipulation
campaign, taking a closer look at users who re-shared the posts produced on
Twitter by the Russian troll accounts publicly disclosed by U.S. Congress
investigation. We collected a dataset with over 43 million election-related
posts shared on Twitter between September 16 and October 21, 2016, by about 5.7
million distinct users. This dataset included accounts associated with the
identified Russian trolls. We use label propagation to infer the ideology of
all users based on the news sources they shared. This method enables us to
classify a large number of users as liberal or conservative with precision and
recall above 90%. Conservatives retweeted Russian trolls about 31 times more
often than liberals and produced 36x more tweets. Additionally, most retweets
of troll content originated from two Southern states: Tennessee and Texas.
Using state-of-the-art bot detection techniques, we estimated that about 4.9%
and 6.2% of liberal and conservative users respectively were bots. Text
analysis on the content shared by trolls reveals that they had a mostly
conservative, pro-Trump agenda. Although an ideologically broad swath of
Twitter users was exposed to Russian Trolls in the period leading up to the
2016 U.S. Presidential election, it was mainly conservatives who helped amplify
their message
Adaptive transient solution of nonuniform multiconductor transmission lines using wavelets
AbstractāThis paper presents a highly adaptive algorithm for the transient simulation of nonuniform interconnects loaded with arbitrary nonlinear and dynamic terminations. The discretization of the governing equations is obtained through a weak formula-tion using biorthogonal wavelet bases as trial and test functions. It is shown how the multiresolution properties of wavelets lead to very sparse approximations of the voltages and currents in typical transient analyzes. A simple yet effective timeāspace adaptive al-gorithm capable of selecting the minimal number of unknowns at each time iteration is described. Numerical results show the high degree of adaptivity of the proposed scheme. Index TermsāElectromagnetic (EM) transient analysis, multi-conductor transmission lines (TLs), wavelet transforms. I
LATERAL HETEROGENEITY AND ARCHITECTURAL ANALYSIS OF THE WALL CREEK MEMBER OF THE UPPER CRETACEOUS (TURONIAN) FRONTIER FORMATION
The Upper Turonian Wall Creek Member (WCM) of the Frontier Formation is part of a series of marine sandstones that were deposited on the western flank of the Cretaceous Western Interior Seaway (KWIS). The KWIS was a low accommodation shallow-marine foreland basin system that included many large deltaic complexes on its western margin. Deposition of WCM deltaic deposits was strongly influenced by fourthorder glacioeustatic cycles, oceanographic circulation patterns, and tectonics related to the active Sevier fold and thrust belt to the west. An in-depth field study of the WCM was performed on the western flank of the Powder River Basin (PRB), WY, in exposures forming the eastern flank of the Tisdale Anticline, a Laramide structure. The goal of the field study is to document the lateral and vertical heterogeneities within the WCM sandstone, its architectural elements, and its stratigraphic surfaces and use these to develop a sequence stratigraphic framework. Results of this study improve the understanding of depositional processes of the WCM and its characterization as a petroleum reservoir within ~30km of active drilling and production of the WCM in the PRB. This study describes 8 facies: 1) laminated mudstone 2) interbedded siltstone and sandstone 3) hummocky cross-stratification 4) low-angle stratified sandstone 5) thinly interbedded sandstone and siltstone 6) heterolithic cross-bedded sandstone 7) mediumgrained heterolithic cross-bedded sandstone and 8) trough cross-bedded sandstone. These facies are consolidated into 4 facies associations: FA1) prodelta FA2) distal delta front FA3) middle delta front FA4) tidal bars/shoals. Facies characteristics, facies stacking patterns, and architectural surfaces/elements indicate two primary deltaic influences: 1) storm/wave dominated deltas and 2) tidally dominated deltas. Three incomplete stratigraphic sequences are observed from facies stacking patterns and stratal geometries. Sequence 1) transgressive systems tract 1 (TST1), highstand systems tract 1 (HST1), and falling stage systems tract 1 (FSST1); Sequence 2) transgressive systems tract 2 (TST2) and highstand systems tract 2 (HST2); Sequence 3) lowstand systems tract 1 (LST1)
Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge
Microbial communities and their associated metabolic activity in
marine sediments have a profound impact on global biogeochemical
cycles. Their composition and structure are attributed to geochemical
and physical factors, but finding direct correlations has remained a
challenge. Here we show a significant statistical relationship between
variation in geochemical composition and prokaryotic community
structure within deep-sea sediments. We obtained comprehensive
geochemical data from two gravity cores near the hydrothermal
vent field Lokiās Castle at the Arctic Mid-Ocean Ridge, in the Norwegian-
Greenland Sea. Geochemical properties in the rift valley
sediments exhibited strong centimeter-scale stratigraphic variability.
Microbial populations were profiled by pyrosequencing from
15 sediment horizons (59,364 16S rRNA gene tags), quantitatively
assessed by qPCR, and phylogenetically analyzed. Although the
same taxa were generally present in all samples, their relative
abundances varied substantially among horizons and fluctuated
between Bacteria- and Archaea-dominated communities. By independently
summarizing covariance structures of the relative
abundance data and geochemical data, using principal components
analysis, we found a significant correlation between changes in
geochemical composition and changes in community structure.
Differences in organic carbon and mineralogy shaped the relative
abundance of microbial taxa. We used correlations to build hypotheses
about energy metabolisms, particularly of the Deep Sea Archaeal
Group, specific Deltaproteobacteria, and sediment lineages
of potentially anaerobic Marine Group I Archaea. We demonstrate
that total prokaryotic community structure can be directly correlated
to geochemistry within these sediments, thus enhancing our
understanding of biogeochemical cycling and our ability to predict
metabolisms of uncultured microbes in deep-sea sediments
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