2,171 research outputs found

    Computing the Fréchet Distance with a Retractable Leash

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    All known algorithms for the Fréchet distance between curves proceed in two steps: first, they construct an efficient oracle for the decision version; second, they use this oracle to find the optimum from a finite set of critical values. We present a novel approach that avoids the detour through the decision version. This gives the first quadratic time algorithm for the Fréchet distance between polygonal curves in (Formula presented.) under polyhedral distance functions (e.g., (Formula presented.) and (Formula presented.)). We also get a (Formula presented.)-approximation of the Fréchet distance under the Euclidean metric, in quadratic time for any fixed (Formula presented.). For the exact Euclidean case, our framework currently yields an algorithm with running time (Formula presented.). However, we conjecture that it may eventually lead to a faster exact algorithm

    Star Routing: Between Vehicle Routing and Vertex Cover

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    We consider an optimization problem posed by an actual newspaper company, which consists of computing a minimum length route for a delivery truck, such that the driver only stops at street crossings, each time delivering copies to all customers adjacent to the crossing. This can be modeled as an abstract problem that takes an unweighted simple graph G=(V,E)G = (V, E) and a subset of edges XX and asks for a shortest cycle, not necessarily simple, such that every edge of XX has an endpoint in the cycle. We show that the decision version of the problem is strongly NP-complete, even if GG is a grid graph. Regarding approximate solutions, we show that the general case of the problem is APX-hard, and thus no PTAS is possible unless P == NP. Despite the hardness of approximation, we show that given any α\alpha-approximation algorithm for metric TSP, we can build a 3α3\alpha-approximation algorithm for our optimization problem, yielding a concrete 9/29/2-approximation algorithm. The grid case is of particular importance, because it models a city map or some part of it. A usual scenario is having some neighborhood full of customers, which translates as an instance of the abstract problem where almost every edge of GG is in XX. We model this property as EX=o(E)|E - X| = o(|E|), and for these instances we give a (3/2+ε)(3/2 + \varepsilon)-approximation algorithm, for any ε>0\varepsilon > 0, provided that the grid is sufficiently big.Comment: Accepted to the 12th Annual International Conference on Combinatorial Optimization and Applications (COCOA'18

    A behavioural intervention increases physical activity in people with subacute spinal cord injury: a randomised trial

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    AbstractQuestions: For people with subacute spinal cord injury, does rehabilitation that is reinforced with the addition of a behavioural intervention to promote physical activity lead to a more active lifestyle than rehabilitation alone? Design: Randomised, controlled trial with concealed allocation, intention-to-treat analysis, and blinded assessors. Participants: Forty-five adults with subacute spinal cord injury who were undergoing inpatient rehabilitation and were dependent on a manual wheelchair. The spinal cord injuries were characterised as: tetraplegia 33%; motor complete 62%; mean time since injury 150 days (SD 74). Intervention: All participants received regular rehabilitation, including handcycle training. Only the experimental group received a behavioural intervention promoting an active lifestyle after discharge. This intervention involved 13 individual sessions delivered by a coach who was trained in motivational interviewing; it began 2 months before and ended 6 months after discharge from inpatient rehabilitation. Outcome measures: The primary outcome was physical activity, which was objectively measured with an accelerometer-based activity monitor 2 months before discharge, at discharge, and 6 and 12 months after discharge from inpatient rehabilitation. The accelerometry data were analysed as total wheeled physical activity, sedentary time and motility. Self-reported physical activity was a secondary outcome. Results: The behavioural intervention significantly increased wheeled physical activity (overall between-group difference from generalised estimating equation 21minutes per day, 95% CI 8 to 35). This difference was evident 6 months after discharge (28minutes per day, 95% CI 8 to 48) and maintained at 12 months after discharge (25minutes per day, 95% CI 1 to 50). No significant intervention effect was found for sedentary time or motility. Self-reported physical activity also significantly improved. Conclusion: The behavioural intervention was effective in eliciting a behavioural change toward a more active lifestyle among people with subacute spinal cord injury. Trial registration: NTR2424. [Nooijen CFJ, Stam H, Bergen MP, Bongers-Janssen HMH, Valent L, van Langeveld S, Twisk J, Act-Active Research Group, van den Berg-Emons RJG (2016) A behavioural intervention increases physical activity in people with subacute spinal cord injury: a randomised trial. Journal of Physiotherapy 62: 35–41

    Evaluation of a website providing information on regional health care services for patients with rheumatoid arthritis: an observational study

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    Studies on the effectiveness of information provision for patients with arthritis through the Internet are scarce. This study aimed to describe rheumatoid arthritis (RA) patients’ knowledge and information needs before and after launching a website providing information on regional health care services for patients with rheumatic conditions. The intervention consisted of a weekly updated website comprising practical information on regional health care services for patients with arthritis. In addition, patients were offered information leaflets and an information meeting. Before (T1) and 24 months after (T2) the website was launched, a random sample of 400 RA patients filled in a questionnaire regarding knowledge and information need (scores 0–18) about accessibility and contents of 18 regional health care services. Two hundred and fifty-one patients returned the questionnaire (response rate 63%) at T1 and 200 patients (50%) at T2, respectively, with 160 paired observations (112 females (70%), mean age 60.4 years (SD 9.9)). The total score for insufficient knowledge about contents decreased from 9.3 (SD 4.9) to 8.5 (SD 4.8; p = 0.03) and for accessibility from 8.6 (SD 4.7) to 8.4 (SD 4.9; p = 0.59). Total score for information need about contents decreased from 4.2 (SD 4.5) to 1.9 (SD 2.9; p < 0.01) and for accessibility from 3.6 (SD 4.5) to 1.4 (SD 2.4; p < 0.01) (paired t-tests)

    Modified bathroom scale and balance assessment: a comparison with clinical tests

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    Frailty and detection of fall risk are major issues in preventive gerontology. A simple tool frequently used in daily life, a bathroom scale (balance quality tester: BQT), was modified to obtain information on the balance of 84 outpatients consulting at a geriatric clinic. The results computed from the BQT were compared to the values of three geriatric tests that are widely used either to detect a fall risk or frailty (timed get up and go: TUG; 10 m walking speed: WS; walking time: WT; one-leg stand: OS). The BQT calculates four parameters that are then scored and weighted, thus creating an overall indicator of balance quality. Raw data, partial scores and the global score were compared with the results of the three geriatric tests. The WT values had the highest correlation with BQT raw data (r = 0.55), while TUG (r = 0.53) and WS (r = 0.56) had the highest correlation with BQT partial scores. ROC curves for OS cut-off values (4 and 5 s) were produced, with the best results obtained for a 5 s cut-off, both with the partial scores combined using Fisher's combination (specificity 85 %: 0.48), and with the empirical score (specificity 85 %: 8). A BQT empirical score of less than seven can detect fall risk in a community dwelling population

    Genome-wide analyses for personality traits identify six genomic loci and show correlations with psychiatric disorders

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    Personality is influenced by genetic and environmental factors1 and associated with mental health. However, the underlying genetic determinants are largely unknown. We identified six genetic loci, including five novel loci2,3, significantly associated with personality traits in a meta-analysis of genome-wide association studies (N = 123,132–260,861). Of these genomewide significant loci, extraversion was associated with variants in WSCD2 and near PCDH15, and neuroticism with variants on chromosome 8p23.1 and in L3MBTL2. We performed a principal component analysis to extract major dimensions underlying genetic variations among five personality traits and six psychiatric disorders (N = 5,422–18,759). The first genetic dimension separated personality traits and psychiatric disorders, except that neuroticism and openness to experience were clustered with the disorders. High genetic correlations were found between extraversion and attention-deficit– hyperactivity disorder (ADHD) and between openness and schizophrenia and bipolar disorder. The second genetic dimension was closely aligned with extraversion–introversion and grouped neuroticism with internalizing psychopathology (e.g., depression or anxiety)

    Effects of cyclooxygenase-1 and -2 gene disruption on Helicobacter pylori-induced gastric inflammation

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    Background. Cyclooxygenases (COXs) play important roles in inflammation and carcinogenesis. The present study aimed to determine the effects of COX-1 and COX-2 gene disruption on Helicobacter pylori-induced gastric inflammation. Methods. Wild-type (WT), COX-1 and COX-2 heterozygous (COX-1 +/- and COX-2 +/-), and homozygous COX-deficient (COX-1 -/- and COX-2 -/-) mice were inoculated with H. pylori strain TN2 and killed after 24 weeks of infection. Uninfected WT and COX-deficient mice were used as controls. Levels of gastric mucosal inflammation, epithelial cell proliferation and apoptosis, and cytokine expression were determined. Results. COX deficiency facilitated H. pylori-induced gastritis. In the presence of H. pylori infection, apoptosis was increased in both WT and COX-deficient mice, whereas cell proliferation was increased in WT and COX-1-deficient, but not in COX-2-deficient, mice. Tumor necrosis factor (TNF)-α and interleukin-10 mRNA expression was elevated in H. pylori-infected mice, but only TNF-α mRNA expression was further increased by COX deficiency. Prostaglandin E 2 levels were increased in infected WT and COX-2-deficient mice but were at very low levels in infected COX-1-deficient mice. Leukotriene (LT) B 4 and LTC 4 levels were increased to a similar extent in infected WT and COX-deficient mice. Conclusions. COX deficiency enhances H. pylori-induced gastritis, probably via TNF-α expression. COX-2, but not COX-1, deficiency suppresses H. pylori-induced cell proliferation. © 2006 by the Infectious Diseases Society of America. All rights reserved.published_or_final_versio
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