111 research outputs found
Trap catch data are poor predictors of damage caused by pine weevil (Hylobius abietis) to conifer seedlings
Damage to planted conifer seedlings caused by the pine weevil Hylobius abietis (L.) is a severe and persistent threat to successful forest regeneration in Europe. Various countermeasures are available, which vary in effectiveness, costs and environmental impact, but none are ideal for all situations. Therefore, there is strong interest in robust assessments of damage risks, as they would enable more cost-effective and environmentally friendly forest pest management. It has been suggested that numbers of adult pine weevils caught in host-odour baited traps placed in regeneration sites may be valuable in such risk assessments. However, published studies provide at most weak support for the hypothesis that trap catch data provide adequate predictions of damage. Therefore, we conducted a two-year field study, designed to determine the relationship between weevil trap catch and subsequent damage at 10 regeneration sites in central Sweden. Site factors that might influence pine weevil feeding on seedlings were recorded and used as explanatory variables in the analysis. Stoniness was the only site factor identified as having a significant effect; damage mainly increased with increases in stoniness. No significant correlation was detected between damage to planted conifer seedlings and numbers of pine weevils trapped in the same locations. We suggest that this lack of correlation between weevil numbers and damage is due to planted seedlings only constituting a minor part of the weevils food intake and considerable between-site variation in availability of food sources other than seedlings. Therefore, assessment of pine weevil numbers appears unlikely to be useful for predicting damage risk at specific regeneration sites
Eliminating Recursion from Monadic Datalog Programs on Trees
We study the problem of eliminating recursion from monadic datalog programs
on trees with an infinite set of labels. We show that the boundedness problem,
i.e., determining whether a datalog program is equivalent to some nonrecursive
one is undecidable but the decidability is regained if the descendant relation
is disallowed. Under similar restrictions we obtain decidability of the problem
of equivalence to a given nonrecursive program. We investigate the connection
between these two problems in more detail
An Exponential Lower Bound for the Latest Deterministic Strategy Iteration Algorithms
This paper presents a new exponential lower bound for the two most popular
deterministic variants of the strategy improvement algorithms for solving
parity, mean payoff, discounted payoff and simple stochastic games. The first
variant improves every node in each step maximizing the current valuation
locally, whereas the second variant computes the globally optimal improvement
in each step. We outline families of games on which both variants require
exponentially many strategy iterations
A Decidable Extension of Data Automata
Data automata on data words is a decidable model proposed by Boja\'nczyk et
al. in 2006. Class automata, introduced recently by Boja\'nczyk and Lasota, is
an extension of data automata which unifies different automata models on data
words. The nonemptiness of class automata is undecidable, since class automata
can simulate two-counter machines. In this paper, a decidable model called
class automata with priority class condition, which restricts class automata
but strictly extends data automata, is proposed. The decidability of this model
is obtained by establishing a correspondence with priority multicounter
automata. This correspondence also completes the picture of the links between
various class conditions of class automata and various models of counter
machines. Moreover, this model is applied to extend a decidability result of
Alur, Cern\'y and Weinstein on the algorithmic analysis of array-accessing
programs.Comment: In Proceedings GandALF 2011, arXiv:1106.081
Sekretariatet för selektivt fiske
Under hösten/vintern 2015/2016 genomförde sekretariatet för selektivt fiske,vid institutionen för akvatiska resurser (SLU-Aqua) tillsammans med svenskt yrkesfiske, nio projekt inom ramen för regeringsuppdraget selektivt fiske. Den övergripande målsättningen för alla projekt inom selektivt fiske är att underlätta införandet av den landningsskyldighet som beslutats i och med reformen av EU:s gemensamma fiskeripolitik. Projekten syftade därför till att minska oönskad fångst i svenskt fiske antingen genom att utveckla befintliga fiskemetoder (framförallt inom trålfiske) eller genom att utveckla alternativa fiskemetoder (främst passiva redskap såsom fällor och burar).
1. "Kombinationsrist för utsortering av fisk och små räkor" (HaV Dnr 1718-15)
2. ”Selektivitet anpassad för små räktrålare” (HaV Dnr 1488-16)
3. "Räkburar” (HaV Dnr 1892-15)
4. ”Vidareutveckling av storleksselektiv kräftrist Halland” (HaV Dnr 1717-15)
5. ”Trål för fångst av plattfisk och stor torsk-rist/stormaskig trål” (HaV Dnr
1716-15)
6. "Förbättrad selektivitet i torsktrålar i Östersjön" (HaV Dnr 2384-15)
7. "Utsortering av gråsej i pelagiska trålar" (HaV Dnr 1715-15)
8. "Selektiv laxfälla" (HaV Dnr 1713-15)
9. "Multifunktionsburar" (HaV Dnr 1712-15)
Projekten genomfördes genom att förslag togs fram gemensamt av SLU-Aqua och näringen utifrån fiskets uttryckliga behov och idéer. Projektförslagen prioriterades och beslutades av en särskild styrgrupp på Havs- och vattenmyndigheten
(HaV), varefter SLU-Aqua upphandlade utförare och agerade projektledare. Vinnande part ansvarade sedan för att anskaffa och utveckla respektive projektidé
enligt projektplanen med stöd från sekretariatet.
Projekten avslutades genom en vetenskaplig utvärdering där personal från SLUAqua deltog i ett experimentellt fiske där det nyutvecklade redskapets fångstegenskaper dokumenterades och analyserades under kommersiella fiskeförhållanden
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