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  • 1
    Electronic Resource
    Electronic Resource
    Visibility with Multiple Reflections (1998)
    Springer
    Discrete & computational geometry 20 (1998), S. 61-78 
    Details
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We show that the region lit by a point light source inside a simple n -gon after at most k reflections off the boundary has combinatorial complexity O(n 2k ) , for any k≥ 1 . A lower bound of Ω ((n/k-Θ(1)) 2k ) is also established which matches the upper bound for any fixed k . A simple near-optimal algorithm for computing the illuminated region is presented, which runs in O(n 2k log n) time and O(n 2k ) space for k〉1 , and in O(n 2 log 2 n) time and O(n 2 ) space for k=1 .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009378
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  • 2
    Electronic Resource
    Electronic Resource
    Extremal Problems for Geometric Hypergraphs (1998)
    Springer
    Discrete & computational geometry 19 (1998), S. 473-484 
    Details
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. A geometric hypergraph H is a collection of i -dimensional simplices, called hyperedges or, simply, edges, induced by some (i+1) -tuples of a vertex set V in general position in d -space. The topological structure of geometric graphs, i.e., the case d=2 , i=1 , has been studied extensively, and it proved to be instrumental for the solution of a wide range of problems in combinatorial and computational geometry. They include the k -set problem, proximity questions, bounding the number of incidences between points and lines, designing various efficient graph drawing algorithms, etc. In this paper, we make an attempt to generalize some of these tools to higher dimensions. We will mainly consider extremal problems of the following type. What is the largest number of edges (i -simplices) that a geometric hypergraph of n vertices can have without containing certain forbidden configurations? In particular, we discuss the special cases when the forbidden configurations are k intersecting edges, k pairwise intersecting edges, k crossing edges, k pairwise crossing edges, k edges that can be stabbed by an i -flat, etc. Some of our estimates are tight.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009365
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  • 3
    Electronic Resource
    Electronic Resource
    Visibility with One Reflection (1998)
    Springer
    Discrete & computational geometry 19 (1998), S. 553-574 
    Details
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We extend the concept of the polygon visible from a source point S in a simple polygon by considering visibility with two types of reflection, specular and diffuse. In specular reflection a light ray reflects from an edge of the polygon according to the rule: the angle of incidence equals the angle of reflection. In diffuse reflection a light ray reflects from an edge of the polygon in all inward directions. Several geometric and combinatorial properties of visibility polygons under these two types of reflection are described, when at most one reflection is permitted. We show that the visibility polygon Vs(S) under specular reflection may be nonsimple, while the visibility polygon Vd(S) under diffuse reflection is always simple. We present a Θ(n 2 ) worst-case bound on the combinatorial complexity of both Vs(S) and Vd(S) and describe simple O(n 2 log 2 n) time algorithms for constructing the sets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009368
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  • 4
    Electronic Resource
    Electronic Resource
    Improved Bounds for Planar k -Sets and Related Problems (1998)
    Springer
    Discrete & computational geometry 19 (1998), S. 373-382 
    Details
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We prove an O(n(k+1) 1/3 ) upper bound for planar k -sets. This is the first considerable improvement on this bound after its early solution approximately 27 years ago. Our proof technique also applies to improve the current bounds on the combinatorial complexities of k -levels in the arrangement of line segments, k convex polygons in the union of n lines, parametric minimum spanning trees, and parametric matroids in general. 〈lsiheader〉 〈onlinepub〉26 June, 1998 〈editor〉Editors-in-Chief: &lsilt;a href=../edboard.html#chiefs&lsigt;Jacob E. Goodman, Richard Pollack&lsilt;/a&lsigt; 〈pdfname〉19n3p373.pdf 〈pdfexist〉yes 〈htmlexist〉no 〈htmlfexist〉no 〈texexist〉yes 〈sectionname〉 〈/lsiheader〉
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009354
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Sintering Duration on the Thermal Conductivity of (Bi, Pb)-2223 Superconducting Pellets Between 10 and 150 K (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 279-284 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductors ; (Bi0.8Pb0.2)2Sr2Ca2Cu3O9.8+δ thermal conductivity ; sintering condition ; phonon thermal conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The influence of sintering duration on the electrical resistivities and thermal conductivities of (Bi0.8Pb0.2)2Sr2Ca2Cu3O9.8+δ pellets with 0.11 〈 δ 〈 0.54 is reported between 10 and 150 K. The results indicate a gradual transformation of the 2212 phase to the 2223 phase and this transformation starts within 5 h of sintering in air at 840°C. The thermal conductivity of the pellets sintered for shorter durations display two maxima at T c0 and around 110 K, respectively. The shape and magnitude of these maxima depend on the relative amount of the 2212 and 2223 phases present in the pellets. While the magnitude of the total thermal conductivity over the measured temperature range is strongly influenced by the duration of sintering, the phonon-dominant nature of heat transport is retained. The relative contribution of the electronic part (λE) to the total thermal conductivity (λ) remains small and does not change appreciably with sintering time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022692119723
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  • 6
    Electronic Resource
    Electronic Resource
    Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 367-372 
    Details
    ISSN: 1572-9605
    Keywords: Thermoelectric power ; electrical resistivity ; high-T c superconductors ; deoxygenation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The thermal variation of the electrical resistivity and thermoelectric power of Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022602931513
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  • 7
    Electronic Resource
    Electronic Resource
    Thermal Conductivity of 2223 BSCCO Superconductor–Polyethylene Glycol Composites Between 20 and 300 K (2000)
    Springer
    Journal of superconductivity 13 (2000), S. 417-422 
    Details
    ISSN: 1572-9605
    Keywords: (Bi,Pb)2223-PEG composites ; thermal conductivity ; polyethylene glycol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Thermal conductivity measurements have been taken between 20 and 300 K on composites prepared from polyethylene glycol (PEG) containing various amounts of superconducting (Bi,Pb)2223 powder. The nature of temperature variation of thermal conductivity (λC) of the composites and its magnitude depend strongly on the volume concentration of the high-temperature superconductor (HTSC) filler present in the material. The results have been discussed in the light of models known for polymer–metal powder composites. It is shown that for composites with 2223 powder content 〈44 vol. %, the measured data can be accounted well with Hamilton–Crosser model, taking the sphericity factor into consideration. Failure of Hamilton–Crosser expression for composites with higher filler concentration is thought to be associated with direct contact between the superconducting grains, which shortcircuits the acoustic mismatch resistance in the composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007755125840
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  • 8
    Electronic Resource
    Electronic Resource
    Nature of thermodynamic fluctuations in the electrical conductivity of Y-Ba-Cu-O pellets and tapes containing silver (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 405-409 
    Details
    ISSN: 1572-9605
    Keywords: (YBa2Cu3.05O x )Ag n pellets and tapes ; thermodynamic fluctuations ; excess electrical conductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Results on the temperature dependence of the electrical resistivity of single-phase silver-doped Y-Ba-Cu-O pellets and tapes, prepared by a coprecipitation technique, are presented. The excess electrical conductivity nearT〉T c is analyzed using Aslamzov-Larkin (AL) formulations. Silver addition in Y-Ba-Cu-O influences strongly the temperature range of both the 3D and 2D regions. The lower limit of the breakdown temperature of the mean-field region (x=−0.5) shifts toward higher temperatures as the concentration of Ag increases in Y-Ba-Cu-O. For samples with higher Ag contents, a third region with critical exponent 〈x〉=−0.28 is seen beyond the mean-field region. This possibly indicates the appearance of a fully critical 3D region, where dynamic scaling theory applies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617466
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  • 9
    Electronic Resource
    Electronic Resource
    Alternating Current Losses in Ag-Sheathed (Bi, Pb)-2223 Multifilamentary Tape at Liquid-Nitrogen Temperature (1998)
    Springer
    Journal of superconductivity 11 (1998), S. 443-447 
    Details
    ISSN: 1572-9605
    Keywords: Ac losses ; (Bi, Pb)-2223 ; tape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The alternating current losses have been investigated at 77 K on the silver-sheathed (Bi, Pb)-2223 multifilamentary tape having 37 filaments using an inductive technique under ac magnetic field with frequencies between 100 and 510 Hz. The measured data on the multifilamentary tape have been discussed vis-à-vis that reported for monofilamentary tapes. The results obtained could be accounted fairly well by considering contributions from the eddy current losses in the silver matrix along with the hysteresis losses in the superconducting filaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022601815911
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal Transport in BPSCCO System Between 20 and 170 K (2000)
    Springer
    Journal of superconductivity 13 (2000), S. 617-621 
    Details
    ISSN: 1572-9605
    Keywords: thermal conductivity ; (Bi,Pb) 2223 pellet ; thermal conductivity peak ; phonon + electron approach
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Thermal conductivity of superconducting (Bi,Pb)2223 pellet in the temperature range 20–170 K is reported. Electronic contribution to thermal conductivity in the normal state is estimated to be ∼25%. Considering both phonon and phonon + electron approach, we attempted to examine the observed nature of the temperature dependence of thermal conductivity. Our analysis strongly supports the role of phonons as well as electrons in the origin of the thermal conductivity peak in the superconducting state. Some of the microscopic quantities evaluated from the best-fit parameters obtained from phonon + electron approach give reasonable values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007837220525
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