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Maximal Distance (maximal + distance)
Selected AbstractsThe ontogeny of foragwehaviour in desert ants, Cataglyphis bicolorECOLOGICAL ENTOMOLOGY, Issue 2 2004Rüdiger Wehner Abstract. 1. Individually foraging desert ants, Cataglyphis bicolor, exhibit short foraging lives (half lifetime, i.e. half-time of the exponential decay function: 4.5 days), in which they perform 3.7 ± 1.9 foraging runs per day. 2. During their short lifetime foraging period the ants increase the duration of their foraging round trips (up to 40.0 ± 24.6 min per run), the maximal distance of individual foraging runs (up to 28.2 ± 4.1 m), and their foraging success, i.e. the ratio of successful runs to the total number of runs (up to 0.70). 3. The parameter that increases most dramatically during a forager's lifetime is direction fidelity, i.e. the tendency to remain faithful to a particular foraging direction. 4. A model based on some simple behavioural rules is used to describe the experimental findings that within an isotropic food environment individual ants develop spatial foraging idiosyncrasies, and do so at a rate that increases with the food densities they encounter. 5. Finally, it is argued that in functional terms direction fidelity is related to the navigational benefits resulting from exploiting familiar (route-based) landmark information, and hence reduces round-trip time and by this physiological stress and predatory risk. [source] Heritability of left atrial size in the Tecumseh populationEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 7 2002P. Palatini Abstract Background ,Little is known about the determinants of atrial size, and no study has analyzed whether genetic factors are involved in the pathogenesis of LA enlargement. Materials and methods We studied the heritability of echocardiographic left atrial size in 290 parents from the Tecumseh Blood Pressure Study and 251 children from the Tecumseh Offspring Study. All data from the parents and children were obtained at the same field office in Tecumseh, USA. Left atrial dimension was determined echocardiographically in accordance with American Society of Echocardiography guidelines with the use of leading-edge-to-leading-edge measurements of the maximal distance between the posterior aortic root wall and the posterior left atrial wall at end systole. Results For correlation between the left atrial dimensions of the parents and their offspring, several models were generated to adjust the atrial dimensions in both groups for an increasing number of clinical variables. After removing the effect of age, gender, height, weight, skinfold thickness, and systolic blood pressure, parent,child correlation for left atrial size was 0·19 (P = 0·007). Further adjustment for left ventricular mass and for measuring left ventricular diastolic function increased the correlation to 0·25 (P = 0·001). Conclusions ,The present data indicate that heredity can explain a small but definite proportion of the variance in left atrial dimension. [source] Conduction Characteristics at the Crista Terminalis During Onset of Pulmonary Vein Atrial FibrillationJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 8 2004SIMON P. FYNN M.D. Introduction: Focal atrial fibrillation (AF) may initiate with an irregular rapid burst of atrial ectopic (AE) activity from a pulmonary vein (PV) focus, but how AF is maintained it is not known. The crista terminalis (CT) is an important line of block in atrial flutter (AFL), but its role in AF has not been determined. The aim of this study was to examine the conduction properties of the CT during onset of AF. Methods and Results: In 10 patients (mean age 38 ± 8 years), we analyzed conduction across the CT during onset of focal AF from an arrhythmogenic PV and during pacing from the same PV at cycle lengths of 700 and 300 ms. A 20-pole catheter was positioned on the CT using intracardiac echocardiography. In 10 control patients with no history of AF, we analyzed conduction across the CT during pacing from the distal coronary sinus at 700 and 300 ms. In all 10 AF patients, AF was initiated with 1 to 9 AE beats (median 5) from a PV. During sinus rhythm, there were no split components (SC) recorded on the CT. During PV AE activity, discrete SC were recorded on the CT in all patients over 6.3 ± 0.9 bipoles (3.7 ± 0.3 cm). Maximal splitting of SC was 66 ± 31 ms (37,139). There was an inverse relationship between AE coupling intervals and the degree of splitting between SC in all patients. Degeneration to AF was preceded by progressive decrement across the CT. SC were recorded during PV pacing at 700 and 300 ms (maximal distance between SC of 24 ± 3 ms and 43 ± 5 ms, respectively, P < 0.001). Maximum SC at CT in controls was 13 ± 8 ms at 700 ms (P = 0.06 vs AF patients) and 16 ± 9 ms at 300 ms (P < 0.01 vs AF patients). Conclusion: (1) These observations provide evidence of anisotropic, decremental conduction across the CT during onset of focal AF and during pacing from the same PV. A line of functional conduction block develops along this anatomic structure (CT). Whether this line of block acts as an initiator of AF or simply contributes passively to nonuniform fibrillatory conduction is unknown. (2) In some patients with focal AF, development of conduction block along the CT may provide a substrate for typical AFL. [source] Do linear landscape elements in farmland act as biological corridors for pollen dispersal?JOURNAL OF ECOLOGY, Issue 1 2010Anja Van Geert Summary 1.,Habitat fragmentation in agricultural landscapes has reduced the population sizes of many plant species while increasing their spatial isolation. Restoration or maintenance of the connectivity by gene flow between the fragmented patches may be determinant to sustaining viable populations, especially for insect-pollinated species. Functional biological corridors facilitating pollen flow between remnants in a human-dominated matrix might achieve this. 2.,Dye dispersal was investigated for the extremely fragmented insect-pollinated herb Primula vulgaris, using fluorescent dye particles as pollen analogues, in a study site comprising 20 populations, of which 13 pairs were physically connected by a linear landscape elements (LLEs, ditches), and 11 pairs were not connected by an LLE. The dye deposition events were used to fit a model of pollen dispersal at the landscape level. We examined whether existing LLEs in the intensively used agricultural landscape act as functional corridors for pollen dispersal. The effects of LLE length and size and plant density of the recipient population on the dispersal patterns were tested. 3.,Dye dispersal showed a leptokurtic decay distribution, with 80% of the dye transfers occurring at less than 85.1 m, and a maximal distance of 1010.8 m. The mean distance travelled by fluorescent dye particles based on the dye dispersal model was , = 87 m. 4.,Dye dispersal between populations was found to be significantly higher when populations were connected by an LLE, than when populations were unconnected. For the group of population pairs connected by an LLE, dye deposition significantly decreased with the distance to dye source, but was not related to recipient population size and plant density. 5.,Synthesis. Our study is, to our knowledge, the first to demonstrate that existing LLEs in an intensively used farmland may act as functional biological corridors facilitating pollen dispersal through pollinator movements. The maintenance or restoration of a network of populations connected by LLEs, but also by other landscape structures (e.g. population relays in vegetation patches and networks of small elements allowing indirect connections) should be strongly encouraged. [source] Myocardium Extending from the Left Atrium onto the Pulmonary Veins: A Comparison Between Subjects with and Without Atrial FibrillationPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 10 2001MINORU TAGAWA TAGAWA, M., et al.: Myocardium Extending from the Left Atrium onto the Pulmonary Veins: A Comparison Between Subjects with and Without Atrial Fibrillation. Rapid discharges from the myocardium extending from the left atrium onto the pulmonary vein (PV) have been shown to initiate AF, and AF may be eradicated by the catheter ablation within the PV. However, if there is any difference in the distribution patterns of the myocardial sleeve onto the PV between the subjects with and without AF is to be determined. Twenty-one autopsied hearts were examined. Eleven patients previously had AF before death and another 10 patients had normal sinus rhythm as confirmed from the medical records including ECGs before death. After exposing the heart, the distance to the peripheral end of the myocardium was measured from the PV-atrial junction in each PV. Then, the PVs were sectioned and stained and the distal end of myocardium and the distribution pattern were studied. The anteroposterior diameter of the left atrium was also measured. In 74 of 84 PVs, the myocardium extended beyond the PV-atrial junction. The myocardium was localized surrounding the vascular smooth muscle layer forming a myocardial sleeve. The peripheral end of the myocardial sleeve was irregular and the maximal and minimal distances were measured in each PV. The myocardium extended most distally in the superior PVs compared to the inferior ones and the maximal distance to the peripheral end was similar between the AF and non-AF subjects (8.4 ± 2.8 vs 8.7 ± 4.4 mm for the left superior and 6.5 ± 3.5 vs 5.1 ± 3.9 mm for the right superior PV, respectively). A significant difference was found in the maximal distance in the inferior PVs: 7.3 ± 4.6 vs 3.3 ± 2.8 mm for the left (P < 0.05) and 5.7 ± 2.4 vs 1.7 ± 1.9 mm for the right inferior PV (P < 0.001) in the subjects with and without AF, respectively. The diameter of left atrium was slightly dilated in AF patients but insignificantly (4.1 ± 0.1 vs 3.6 ± 0.1 cm, P > 0.07). The myocytes on the PV were less uniform and surrounded by more fibrosis in patients with AF compared to those without AF. In conclusion, the myocardium extended beyond the atrium-vein junction onto the PVs. The distribution patterns of the myocardium was almost similar between subjects with and without AF, but the histology suggested variable myocytes in size and fibrosis in patients with AF. [source] What is the furthest graph from a hereditary property?RANDOM STRUCTURES AND ALGORITHMS, Issue 1 2008Noga Alon Abstract For a graph property P, the edit distance of a graph G from P, denoted EP(G), is the minimum number of edge modifications (additions or deletions) one needs to apply to G to turn it into a graph satisfying P. What is the furthest graph on n vertices from P and what is the largest possible edit distance from P? Denote this maximal distance by ed(n,P). This question is motivated by algorithmic edge-modification problems, in which one wishes to find or approximate the value of EP(G) given an input graph G. A monotone graph property is closed under removal of edges and vertices. Trivially, for any monotone property, the largest edit distance is attained by a complete graph. We show that this is a simple instance of a much broader phenomenon. A hereditary graph property is closed under removal of vertices. We prove that for any hereditary graph property P, a random graph with an edge density that depends on P essentially achieves the maximal distance from P, that is: ed(n,P) = EP(G(n,p(P))) + o(n2) with high probability. The proofs combine several tools, including strengthened versions of the Szemerédi regularity lemma, properties of random graphs and probabilistic arguments. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2008 [source] | |||||||||||||