62,698 research outputs found
Solving -SUM using few linear queries
The -SUM problem is given input real numbers to determine whether any
of them sum to zero. The problem is of tremendous importance in the
emerging field of complexity theory within , and it is in particular open
whether it admits an algorithm of complexity with . Inspired by an algorithm due to Meiser (1993), we show
that there exist linear decision trees and algebraic computation trees of depth
solving -SUM. Furthermore, we show that there exists a
randomized algorithm that runs in
time, and performs linear queries on the input. Thus, we show
that it is possible to have an algorithm with a runtime almost identical (up to
the ) to the best known algorithm but for the first time also with the
number of queries on the input a polynomial that is independent of . The
bound on the number of linear queries is also a tighter bound
than any known algorithm solving -SUM, even allowing unlimited total time
outside of the queries. By simultaneously achieving few queries to the input
without significantly sacrificing runtime vis-\`{a}-vis known algorithms, we
deepen the understanding of this canonical problem which is a cornerstone of
complexity-within-.
We also consider a range of tradeoffs between the number of terms involved in
the queries and the depth of the decision tree. In particular, we prove that
there exist -linear decision trees of depth
Forest Stand Structure and Primary Production in relation to Ecosystem Development, Disturbance, and Canopy Composition
Temperate forests are complex ecosystems that sequester carbon (C) in biomass. C storage is related to ecosystem-scale forest structure, changing over succession, disturbance, and with community composition. We quantified ecosystem biological and physical structure in two forest chronosequences varying in disturbance intensity, and three late successional functional types to examine how multiple structural expressions relate to ecosystem C cycling. We quantified C cycling as wood net primary production (NPP), ecosystem structure as Simpsonâs Index, and physical structure as leaf quantity (LAI) and arrangement (rugosity), examining how wood NPP-structure relates to light distribution and use-efficiency. Relationships between structural attributes of biodiversity, LAI, and rugosity differed. Development of rugosity was conserved regardless of disturbance and composition, suggesting optimization of vegetation arrangement over succession. LAI and rugosity showed significant positive productivity trends over succession, particularly within deciduous broadleaf forests, suggesting these measures of structure contain complementary, not redundant, information related to C cycling
The Complexity of Simultaneous Geometric Graph Embedding
Given a collection of planar graphs on the same set of
vertices, the simultaneous geometric embedding (with mapping) problem, or
simply -SGE, is to find a set of points in the plane and a bijection
such that the induced straight-line drawings of
under are all plane.
This problem is polynomial-time equivalent to weak rectilinear realizability
of abstract topological graphs, which Kyn\v{c}l (doi:10.1007/s00454-010-9320-x)
proved to be complete for , the existential theory of the
reals. Hence the problem -SGE is polynomial-time equivalent to several other
problems in computational geometry, such as recognizing intersection graphs of
line segments or finding the rectilinear crossing number of a graph.
We give an elementary reduction from the pseudoline stretchability problem to
-SGE, with the property that both numbers and are linear in the
number of pseudolines. This implies not only the -hardness
result, but also a lower bound on the minimum size of a
grid on which any such simultaneous embedding can be drawn. This bound is
tight. Hence there exists such collections of graphs that can be simultaneously
embedded, but every simultaneous drawing requires an exponential number of bits
per coordinates. The best value that can be extracted from Kyn\v{c}l's proof is
only
Semi-algebraic Ramsey numbers
Given a finite point set , a -ary semi-algebraic
relation on is the set of -tuples of points in , which is
determined by a finite number of polynomial equations and inequalities in
real variables. The description complexity of such a relation is at most if
the number of polynomials and their degrees are all bounded by . The Ramsey
number is the minimum such that any -element point set
in equipped with a -ary semi-algebraic relation , such
that has complexity at most , contains members such that every
-tuple induced by them is in , or members such that every -tuple
induced by them is not in .
We give a new upper bound for for and fixed.
In particular, we show that for fixed integers , establishing a subexponential upper bound on .
This improves the previous bound of due to Conlon, Fox, Pach,
Sudakov, and Suk, where is a very large constant depending on and
. As an application, we give new estimates for a recently studied
Ramsey-type problem on hyperplane arrangements in . We also study
multi-color Ramsey numbers for triangles in our semi-algebraic setting,
achieving some partial results
The visual preferences for forest regeneration and field afforestation : four case studies in Finland
The overall aim of this dissertation was to study the public's preferences for forest regeneration fellings and field afforestations, as well as to find out the relations of these preferences to landscape management instructions, to ecological healthiness, and to the contemporary theories for predicting landscape preferences. This dissertation includes four case studies in Finland, each based on the visualization of management options and surveys.
Guidelines for improving the visual quality of forest regeneration and field afforestation are given based on the case studies. The results show that forest regeneration can be connected to positive images and memories when the regeneration area is small and some time has passed since the felling. Preferences may not depend only on the management alternative itself but also on the viewing distance, viewing point, and the scene in which the management options are implemented.
The current Finnish forest landscape management guidelines as well as the ecological healthiness of the studied options are to a large extent compatible with the public's preferences. However, there are some discrepancies. For example, the landscape management instructions as well as ecological hypotheses suggest that the retention trees need to be left in groups, whereas people usually prefer individually located retention trees to those trees in groups. Information and psycho-evolutionary theories provide some possible explanations for people's preferences for forest regeneration and field afforestation, but the results cannot be consistently explained by these theories.
The preferences of the different stakeholder groups were very similar. However, the preference ratings of the groups that make their living from forest - forest owners and forest professionals - slightly differed from those of the others. These results provide support for the assumptions that preferences are largely consistent at least within one nation, but that knowledge and a reference group may also influence preferences.VÀitöskirjassa tutkittiin ihmisten maisemapreferenssejÀ (maisemallisia arvostuksia) metsÀnuudistamishakkuiden ja pellonmetsitysten suhteen sekÀ analysoitiin nÀiden preferenssien yhteyksiÀ maisemanhoito-ohjeisiin, vaihtoehtojen ekologiseen terveyteen ja preferenssejÀ ennustaviin teorioihin. VÀitöskirja sisÀltÀÀ neljÀ tapaustutkimusta, jotka perustuvat hoitovaihtoehtojen visualisointiin ja kyselytutkimuksiin.
Tapaustutkimusten pohjalta annetaan ohjeita siitÀ, kuinka uudistushakkuiden ja pellonmetsitysten visuaalista laatua voidaan parantaa. VÀitöskirjan tulokset osoittavat, ettÀ uudistamishakkuut voivat herÀttÀÀ myös myönteisiÀ mielikuvia ja muistoja, jos uudistusala on pieni ja hakkuun vÀlittömÀt jÀljet ovat jo peittyneet. Preferensseihin vaikuttaa hoitovaihtoehdon lisÀksi mm. katseluetÀisyys, katselupiste ja ympÀristö, jossa vaihtoehto on toteutettu.
Eri viiteryhmien (metsÀammattilaiset, pÀÀkaupunkiseudun asukkaat, ympÀristönsuojelijat, tutkimusalueiden matkailijat, paikalliset asukkaat sekÀ metsÀnomistajat) maisemapreferenssit olivat hyvin samankaltaisia. Kuitenkin ne ryhmÀt, jotka saavat ainakin osan elannostaan metsÀstÀ - metsÀnomistajat ja metsÀammattilaiset - pitivÀt metsÀnhakkuita esittÀvistÀ kuvista hieman enemmÀn kuin muut ryhmÀt. NÀmÀ tulokset tukevat oletusta, ettÀ maisemapreferenssit ovat laajalti yhtenevÀisiÀ ainakin yhden kansan tai kulttuurin keskuudessa, vaikka myös viiteryhmÀ saattaa vaikuttaa preferensseihin jonkin verran.
Nykyiset metsÀmaisemanhoito-ohjeet ovat pitkÀlti samankaltaisia tÀssÀ vÀitöskirjassa havaittujen maisemapreferenssien kanssa. MyöskÀÀn tutkittujen vaihtoehtoisten hoitotapojen ekologisen paremmuuden ja niihin kohdistuvien maisemallisten arvostusten vÀlillÀ ei ollut suurta ristiriitaa. Kuitenkin joitakin eroavaisuuksia oli; esimerkiksi sekÀ maisemanhoito-ohjeiden ettÀ ekologisten hypoteesien mukaan sÀÀstöpuut tulisi jÀttÀÀ ryhmiin, kun taas ihmiset pitivÀt eniten yksittÀin jÀtetyistÀ puista. Informaatiomalli ja psyko-evolutionaarinen teoria tarjoavat mahdollisia selityksiÀ uudistushakkuisiin ja pellonmetsitykseen kohdistuville preferensseille, vaikkakaan tutkimuksen tuloksia ei voida tÀysin selittÀÀ nÀillÀ teorioilla
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