167 research outputs found
Deterministic Digital Clustering of Wireless Ad Hoc Networks
We consider deterministic distributed communication in wireless ad hoc
networks of identical weak devices under the SINR model without predefined
infrastructure. Most algorithmic results in this model rely on various
additional features or capabilities, e.g., randomization, access to geographic
coordinates, power control, carrier sensing with various precision of
measurements, and/or interference cancellation. We study a pure scenario, when
no such properties are available. As a general tool, we develop a deterministic
distributed clustering algorithm. Our solution relies on a new type of
combinatorial structures (selectors), which might be of independent interest.
Using the clustering, we develop a deterministic distributed local broadcast
algorithm accomplishing this task in rounds, where
is the density of the network. To the best of our knowledge, this is
the first solution in pure scenario which is only polylog away from the
universal lower bound , valid also for scenarios with
randomization and other features. Therefore, none of these features
substantially helps in performing the local broadcast task. Using clustering,
we also build a deterministic global broadcast algorithm that terminates within
rounds, where is the diameter of the
network. This result is complemented by a lower bound , where is the path-loss parameter of the
environment. This lower bound shows that randomization or knowledge of own
location substantially help (by a factor polynomial in ) in the global
broadcast. Therefore, unlike in the case of local broadcast, some additional
model features may help in global broadcast
An Efficient Local Search for Partial Latin Square Extension Problem
A partial Latin square (PLS) is a partial assignment of n symbols to an nxn
grid such that, in each row and in each column, each symbol appears at most
once. The partial Latin square extension problem is an NP-hard problem that
asks for a largest extension of a given PLS. In this paper we propose an
efficient local search for this problem. We focus on the local search such that
the neighborhood is defined by (p,q)-swap, i.e., removing exactly p symbols and
then assigning symbols to at most q empty cells. For p in {1,2,3}, our
neighborhood search algorithm finds an improved solution or concludes that no
such solution exists in O(n^{p+1}) time. We also propose a novel swap
operation, Trellis-swap, which is a generalization of (1,q)-swap and
(2,q)-swap. Our Trellis-neighborhood search algorithm takes O(n^{3.5}) time to
do the same thing. Using these neighborhood search algorithms, we design a
prototype iterated local search algorithm and show its effectiveness in
comparison with state-of-the-art optimization solvers such as IBM ILOG CPLEX
and LocalSolver.Comment: 17 pages, 2 figure
Íslensk börn og unglingar með höfuðáverka : hve margir þurfa sérhæfða fræðslu, endurhæfingu eða eftirfylgd og hvers konar íhlutun er við hæfi?
Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenTilgangur rannsóknarinnar var að kanna fjölda barna og unglinga, sem lýsa eftirstöðvum fjórum árum eftir höfuðáverka, og skoða eðli þessara kvartana, og meta þannig þörf fyrir sérhæfða íhlutun af mismunandi toga. Gögnum var safnað á framvirkan hátt um alla sjúklinga 0-19 ára, sem greindir voru með höfuðáverka (ICD-9 850-854) á Borgarspítalanum á einu ári, 1992-1993 (n=405). Fjórum árum síðar var spurningalisti um eftirstöðvar áverka sendur til sjúklinga. Alvarleikastig byggt á eðli kvartana var metið samkvæmt viðmiðum Glasgow Outcome Scale (GOS), barnaútgáfu. Alls lýstu 39 sjúklingar lýstu eftirstöðvum höfuðáverka fjórum árum síðar. Samkvæmt viðmiðum GOS lýstu 19 þeirra góðri útkomu (e. good outcome), 14 lýstu miðlungs hömlun (e. moderate disability), 2 lýstu alvarlegri hömlun (severe disability) og 4 höfðu látist vegna heilaskaða. Nýleg athugun bendir til þess að ekki hafi orðið fækkun á börnum og unglingum sem hljóta alvarlegri höfuðáverka (ICD-9 851- 854) á ári hverju.Niðurstöður benda til þess að tugir íslenskra barna og unglinga þarfnist sérhæfðrar íhlutunar og eftirfylgdar á ári hverju vegna afleiðinga höfuðáverka. Íhlutunin getur verið mjög breytileg, allt frá fræðslu fyrir foreldra til endurhæfingar og eftirfylgdar til lengri tíma. Íhlutunin þarf að taka mið af vanda hvers og eins
Structurally Parameterized d-Scattered Set
In -Scattered Set we are given an (edge-weighted) graph and are asked to
select at least vertices, so that the distance between any pair is at least
, thus generalizing Independent Set. We provide upper and lower bounds on
the complexity of this problem with respect to various standard graph
parameters. In particular, we show the following:
- For any , an -time algorithm, where
is the treewidth of the input graph.
- A tight SETH-based lower bound matching this algorithm's performance. These
generalize known results for Independent Set.
- -Scattered Set is W[1]-hard parameterized by vertex cover (for
edge-weighted graphs), or feedback vertex set (for unweighted graphs), even if
is an additional parameter.
- A single-exponential algorithm parameterized by vertex cover for unweighted
graphs, complementing the above-mentioned hardness.
- A -time algorithm parameterized by tree-depth
(), as well as a matching ETH-based lower bound, both for
unweighted graphs.
We complement these mostly negative results by providing an FPT approximation
scheme parameterized by treewidth. In particular, we give an algorithm which,
for any error parameter , runs in time
and returns a
-scattered set of size , if a -scattered set of the same
size exists
On Coloring Resilient Graphs
We introduce a new notion of resilience for constraint satisfaction problems,
with the goal of more precisely determining the boundary between NP-hardness
and the existence of efficient algorithms for resilient instances. In
particular, we study -resiliently -colorable graphs, which are those
-colorable graphs that remain -colorable even after the addition of any
new edges. We prove lower bounds on the NP-hardness of coloring resiliently
colorable graphs, and provide an algorithm that colors sufficiently resilient
graphs. We also analyze the corresponding notion of resilience for -SAT.
This notion of resilience suggests an array of open questions for graph
coloring and other combinatorial problems.Comment: Appearing in MFCS 201
A population-based study of stimulant drug treatment of ADHD and academic progress in children.
To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.We evaluated the hypothesis that later start of stimulant treatment of attention-deficit/hyperactivity disorder adversely affects academic progress in mathematics and language arts among 9- to 12-year-old children. We linked nationwide data from the Icelandic Medicines Registry and the Database of National Scholastic Examinations. The study population comprised 11,872 children born in 1994-1996 who took standardized tests in both fourth and seventh grade. We estimated the probability of academic decline (drop of ≥ 5.0 percentile points) according to drug exposure and timing of treatment start between examinations. To limit confounding by indication, we concentrated on children who started treatment either early or later, but at some point between fourth-grade and seventh-grade standardized tests. In contrast with nonmedicated children, children starting stimulant treatment between their fourth- and seventh-grade tests were more likely to decline in test performance. The crude probability of academic decline was 72.9% in mathematics and 42.9% in language arts for children with a treatment start 25 to 36 months after the fourth-grade test. Compared with those starting treatment earlier (≤ 12 months after tests), the multivariable adjusted risk ratio (RR) for decline was 1.7 (95% confidence interval [CI]: 1.2-2.4) in mathematics and 1.1 (95% CI: 0.7-1.8) in language arts. The adjusted RR of mathematics decline with later treatment was higher among girls (RR, 2.7; 95% CI: 1.2-6.0) than boys (RR, 1.4; 95% CI: 0.9-2.0). Later start of stimulant drug treatment of attention-deficit/hyperactivity disorder is associated with academic decline in mathematicsPfizer
Novartis
University of Iceland
Icelandic Centre for Research (RANNIS
Advanced brain dopamine transporter imaging in mice using small-animal SPECT/CT
Abstract. The stable marriage problem has recently been studied in its general setting, where both ties and incomplete lists are allowed. It is NP-hard to find a stable matching of maximum size, while any stable matching is a maximal matching and thus trivially a factor two approximation. In this paper, we give the first nontrivial result for approximation of factor less than two. Our algorithm achieves an approximation ratio of 2/(1+L −2) for instances in which only men have ties of length at most L. When both men and women are allowed to have ties, we show a ratio of 13/7(< 1.858) for the case when ties are of length two. We also improve the lower bound on the approximation ratio to 2
Environmental pressure from the 2014–15 eruption of Bárðarbunga volcano, Iceland
The effusive six months long 2014-2015 Bárðarbunga eruption (31 August-27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km3 of lava. The total SO2 emission was 11 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO2 exceeded the 350 μg m−3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H2SO4, HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surface
waters, soils, and vegetation of Iceland
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