2,014 research outputs found
On the State Complexity of Partial Derivative Automata For Regular Expressions with Intersection
Extended regular expressions (with complement and intersection) are used in many applications due to their succinctness. In particular, regular expressions extended with intersection only (also called semi-extended) can already be exponentially smaller than standard regular expressions or equivalent nondeterministic finite automata (NFA). For practical purposes it is important to study the average behaviour of conversions between these models. In this paper, we focus on the conversion of regular expressions with intersection to nondeterministic finite automata, using partial derivatives and the notion of support. First, we give a tight upper bound of 2O(n) for the worst-case number of states of the resulting partial derivative automaton, where n is the size of the expression. Using the framework of analytic combinatorics, we then establish an upper bound of (1.056 + o(1))n for its asymptotic average-state complexity, which is significantly smaller than the one for the worst case. (c) IFIP International Federation for Information Processing 2016
A phenomenological description of quantum-gravity-induced space-time noise
I propose a phenomenological description of space-time foam and discuss the
experimental limits that are within reach of forthcoming experiments.Comment: 10 pages, LaTex, 1 figure. Short paper, omitting most technical
details. More detailed analysis was reported in gr-qc/010400
Cortical Factor Feedback Model for Cellular Locomotion and Cytofission
Eukaryotic cells can move spontaneously without being guided by external
cues. For such spontaneous movements, a variety of different modes have been
observed, including the amoeboid-like locomotion with protrusion of multiple
pseudopods, the keratocyte-like locomotion with a widely spread lamellipodium,
cell division with two daughter cells crawling in opposite directions, and
fragmentations of a cell to multiple pieces. Mutagenesis studies have revealed
that cells exhibit these modes depending on which genes are deficient,
suggesting that seemingly different modes are the manifestation of a common
mechanism to regulate cell motion. In this paper, we propose a hypothesis that
the positive feedback mechanism working through the inhomogeneous distribution
of regulatory proteins underlies this variety of cell locomotion and
cytofission. In this hypothesis, a set of regulatory proteins, which we call
cortical factors, suppress actin polymerization. These suppressing factors are
diluted at the extending front and accumulated at the retracting rear of cell,
which establishes a cellular polarity and enhances the cell motility, leading
to the further accumulation of cortical factors at the rear. Stochastic
simulation of cell movement shows that the positive feedback mechanism of
cortical factors stabilizes or destabilizes modes of movement and determines
the cell migration pattern. The model predicts that the pattern is selected by
changing the rate of formation of the actin-filament network or the threshold
to initiate the network formation
Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis
Collectively, phagotrophic algae (mixotrophs) form a functional continuum of nutritional modes between autotrophy and heterotrophy, but the specific physiological benefits of mixotrophic nutrition differ among taxa. Ochromonas spp. are ubiquitous chrysophytes that exhibit high nutritional flexibility, although most species generally fall towards the heterotrophic end of the mixotrophy spectrum. We assessed the sources of carbon and nitrogen in Ochromonas sp. strain BG-1 growing mixotrophically via short-term stable isotope probing. An axenic culture was grown in the presence of either heat-killed bacteria enriched with ^(15)N and ^(13)C, or unlabeled heat-killed bacteria and labeled inorganic substrates (^(13)C-bicarbonate and ^(15)N-ammonium). The alga exhibited high growth rates (up to 2 divisions per day) only until heat-killed bacteria were depleted. NanoSIMS and bulk IRMS isotope analyses revealed that Ochromonas obtained 84–99% of its carbon and 88–95% of its nitrogen from consumed bacteria. The chrysophyte assimilated inorganic ^(13)C-carbon and ^(15)N-nitrogen when bacterial abundances were very low, but autotrophic (photosynthetic) activity was insufficient to support net population growth of the alga. Our use of nanoSIMS represents its first application towards the study of a mixotrophic alga, enabling a better understanding and quantitative assessment of carbon and nutrient acquisition by this species
Constraints on the pMSSM from searches for squarks and gluinos by ATLAS
We study the impact of the jets and missing transverse momentum SUSY analyses
of the ATLAS experiment on the phenomenological MSSM (pMSSM). We investigate
sets of SUSY models with a flat and logarithmic prior in the SUSY mass scale
and a mass range up to 1 and 3 TeV, respectively. These models were found
previously in the study 'Supersymmetry without Prejudice'. Removing models with
long-lived SUSY particles, we show that 99% of 20000 randomly generated pMSSM
model points with a flat prior and 87% for a logarithmic prior are excluded by
the ATLAS results. For models with squarks and gluinos below 600 GeV all models
of the pMSSM grid are excluded. We identify SUSY spectra where the current
ATLAS search strategy is less sensitive and propose extensions to the inclusive
jets search channel
When a 520 million-year-old Chengjiang fossil meets a modern micro-CT - a case study
The 520 million-year-old Chengjiang biota of China (UNESCO World Heritage) presents the earliest known evidence of the so-called Cambrian Explosion. Studies, however, have mainly been limited to the information exposed on the surface of the slabs. Thus far, structures preserved inside the slabs were accessed by careful removal of the matrix, in many cases with the unfortunate sacrifice of some "less important" structures, which destroys elements of exceptionally preserved specimens. Here, we show for the first time that microtomography (micro-CT) can reveal structures situated inside a Chengjiang fossil slab without causing any damage. In the present study a trilobitomorph arthropod (Xandarella spectaculum) can be reliably identified only with the application of micro-CT. We propose that this technique is an important tool for studying three-dimensionally preserved Chengjiang fossils and, most likely, also those from other biota with a comparable type of preservation, specifically similar iron concentrations
Regular Expressions and Transducers over Alphabet-invariant and User-defined Labels
We are interested in regular expressions and transducers that represent word
relations in an alphabet-invariant way---for example, the set of all word pairs
u,v where v is a prefix of u independently of what the alphabet is. Current
software systems of formal language objects do not have a mechanism to define
such objects. We define transducers in which transition labels involve what we
call set specifications, some of which are alphabet invariant. In fact, we give
a more broad definition of automata-type objects, called labelled graphs, where
each transition label can be any string, as long as that string represents a
subset of a certain monoid. Then, the behaviour of the labelled graph is a
subset of that monoid. We do the same for regular expressions. We obtain
extensions of a few classic algorithmic constructions on ordinary regular
expressions and transducers at the broad level of labelled graphs and in such a
way that the computational efficiency of the extended constructions is not
sacrificed. For regular expressions with set specs we obtain the corresponding
partial derivative automata. For transducers with set specs we obtain further
algorithms that can be applied to questions about independent regular
languages, in particular the witness version of the independent property
satisfaction question
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Do emotional difficulties and peer problems hew together from childhood to adolescence? The case of children with a history of developmental language disorder (DLD)
Children and adolescents with developmental language disorder (DLD) are, overall, vulnerable to difficulties in emotional adjustment and in peer relations. However, previous research has shown that different subgroups follow different trajectories in respect of quality of peer relations. Less is known of the trajectories of emotional development. We consider here the possibility that development in these two domains is interrelated: that is, the trajectories of emotional and peer problems will proceed in parallel. We conducted longitudinal joint trajectories analyses of emotional and peer relations in a sample of young people identified as having DLD at age 7 years and seen at intervals up to 16 years. Potential influences on joint trajectory group membership were examined. Findings revealed five distinct joint trajectories. Emotional and peer difficulties do hew together from childhood to adolescence for just over half of the sample, but not all. The variables most clearly associated with group membership were pragmatic language ability, prosociality and parental mental health. This is the first study to examine joint longitudinal trajectories of emotional and peer difficulties in individuals with DLD. We demonstrate that development in individuals with DLD is heterogeneous and identify three key variables associated with personal and social adjustment from childhood to adolescence. Theoretical and clinical implications of these findings are discussed
Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning
Networks of trophic links (food webs) are used to describe and understand mechanistic routes for translocation of energy (biomass) between species. However, a relatively low proportion of ecosystems have been studied using food web approaches due to difficulties in making observations on large numbers of species. In this paper we demonstrate that Machine Learning of food webs, using a logic-based approach called A/ILP, can generate plausible and testable food webs from field sample data. Our example data come from a national-scale Vortis suction sampling of invertebrates from arable fields in Great Britain. We found that 45 invertebrate species or taxa, representing approximately 25% of the sample and about 74% of the invertebrate individuals included in the learning, were hypothesized to be linked. As might be expected, detritivore Collembola were consistently the most important prey. Generalist and omnivorous carabid beetles were hypothesized to be the dominant predators of the system. We were, however, surprised by the importance of carabid larvae suggested by the machine learning as predators of a wide variety of prey. High probability links were hypothesized for widespread, potentially destabilizing, intra-guild predation; predictions that could be experimentally tested. Many of the high probability links in the model have already been observed or suggested for this system, supporting our contention that A/ILP learning can produce plausible food webs from sample data, independent of our preconceptions about “who eats whom.” Well-characterised links in the literature correspond with links ascribed with high probability through A/ILP. We believe that this very general Machine Learning approach has great power and could be used to extend and test our current theories of agricultural ecosystem dynamics and function. In particular, we believe it could be used to support the development of a wider theory of ecosystem responses to environmental change
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