57,644 research outputs found
Revisiting Synthesis for One-Counter Automata
We study the (parameter) synthesis problem for one-counter automata with
parameters. One-counter automata are obtained by extending classical
finite-state automata with a counter whose value can range over non-negative
integers and be tested for zero. The updates and tests applicable to the
counter can further be made parametric by introducing a set of integer-valued
variables called parameters. The synthesis problem for such automata asks
whether there exists a valuation of the parameters such that all infinite runs
of the automaton satisfy some omega-regular property. Lechner showed that (the
complement of) the problem can be encoded in a restricted one-alternation
fragment of Presburger arithmetic with divisibility. In this work (i) we argue
that said fragment, called AERPADPLUS, is unfortunately undecidable.
Nevertheless, by a careful re-encoding of the problem into a decidable
restriction of AERPADPLUS, (ii) we prove that the synthesis problem is
decidable in general and in N2EXP for several fixed omega-regular properties.
Finally, (iii) we give a polynomial-space algorithm for the special case of the
problem where parameters can only be used in tests, and not updates, of the
counter
Revisiting the contribution of transpiration to global terrestrial evapotranspiration
Even though knowing the contributions of transpiration (T), soil and open water evaporation (E), and interception (I) to terrestrial evapotranspiration (ET=T+E+I) is crucial for understanding the hydrological cycle and its connection to ecological processes, the fraction of T is unattainable by traditional measurement techniques over large scales. Previously reported global mean T/(E+T+I) from multiple independent sources, including satellite-based estimations, reanalysis, land surface models, and isotopic measurements, varies substantially from 24% to 90%. Here we develop a new ET partitioning algorithm, which combines global evapotranspiration estimates and relationships between leaf area index (LAI) and T/(E+T) for different vegetation types, to upscale a wide range of published site-scale measurements. We show that transpiration accounts for about 57.2% (with standard deviation6.8%) of global terrestrial ET. Our approach bridges the scale gap between site measurements and global model simulations,and can be simply implemented into current global climate models to improve biological CO2 flux simulations
Fruit and Fish: Alison Goodwinâs Reimaging of the Modernist Motif
Alison Goodwinâs painting Cantaloupe (2008) at ïŹrst appears, perhaps naively, to depict a still life of fruit and ïŹowers on a table: pomegranate, cantaloupe, sunïŹowers, and a drink. Beneath two rusty red and murky green lines, a diamond pattern demarcates the ïŹoor from the wall above. Next to the mottled green-and-red wall is a view through an open window. Three narrow houses lean precariously to the left; the windows are indicated, almost carelessly, by blocks of watery black paint. Two stylized trees with foliage shaped into bulbous spheres punctuate the row of buildings. Goodwinâs particular style, with its emphasis on a skewed perspective, ïŹattened forms, and broadly applied colors, cannotâand should notâbe read as unsophisticated or unknowing. Rather, Goodwinâs paintings reinterpret the work of some of the most important nineteenth- and early twentieth-century painters. She deliberately evokes the style and subjects of European modernists such as Henri Matisse, Paul Gauguin, and Vincent van Gogh. Each of her paintings recalls the implied formal tension between depicted three-dimensional space and the literal ïŹatness of painted planes of color and stylized forms that her predecessors welcomed. Matisse, CĂ©zanne, and others in the late nineteenth century rejected academic norms of picture making (painting realistically through modeling, shade, and one-point perspective). By revisiting these artistsâ aesthetic, Goodwin complicates this historical progression and inserts her own mark onto the modernist (and particularly male-dominated) canon. [excerpt
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