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11.
Pankaj K. Agarwal Herbert Edelsbrunner Otfried Schwarzkopf Emo Welzl 《Discrete and Computational Geometry》1991,6(1):407-422
We present an algorithm to compute a Euclidean minimum spanning tree of a given setS ofN points inE
d
in timeO(F
d
(N,N) log
d
N), whereF
d
(n,m) is the time required to compute a bichromatic closest pair amongn red andm green points inE
d
. IfF
d
(N,N)=Ω(N
1+ε), for some fixed ɛ>0, then the running time improves toO(F
d
(N,N)). Furthermore, we describe a randomized algorithm to compute a bichromatic closest pair in expected timeO((nm logn logm)2/3+m log2
n+n log2
m) inE
3, which yields anO(N
4/3 log4/3
N) expected time, algorithm for computing a Euclidean minimum spanning tree ofN points inE
3. Ind≥4 dimensions we obtain expected timeO((nm)1−1/([d/2]+1)+ε+m logn+n logm) for the bichromatic closest pair problem andO(N
2−2/([d/2]+1)ε) for the Euclidean minimum spanning tree problem, for any positive ɛ.
The first, second, and fourth authors acknowledge support from the Center for Discrete Mathematics and Theoretical Computer
Science (DIMACS), a National Science Foundation Science and Technology Center under NSF Grant STC 88-09648. The second author's
work was supported by the National Science Foundation under Grant CCR-8714565. The third author's work was supported by the
Deutsche Forschungsgemeinschaft under Grant A1 253/1-3, Schwerpunktprogramm “Datenstrukturen und effiziente Algorithmen”.
The last two authors' work was also partially supported by the ESPRIT II Basic Research Action of the EC under Contract No.
3075 (project ALCOM). 相似文献
12.
O. Francescangeli B. Yang M. Laus A. S. Angeloni G. Galli E. Chiellini 《Journal of Polymer Science.Polymer Physics》1995,33(4):699-705
An x-ray investigation on powder specimens and stretched oriented fibers of poly(urethaneester)s TDI-CmCn, derived from various mesogenic alkylene di[4-(ω-hydroxyalkyloxy-4-oxybenzoyl)oxybenzoate]s (CmCn; m = 2, 4, or 6, and n = 4, 6, 8, or 10) and 2, 4-toluenediisocyanate (TDI), is reported. Evidence is provided for the formation of two different nematic mesophases in the polymers, namely a cybotactic nematic and a conventional nematic mesophase. Whereas samples TDI-C2C6, TDI-C6C4, and TDI-C6C10 formed one cybotactic nematic mesophase, samples TDI-C4C6, TDI-C6C6, and TDI-C6C8 exhibited both cybotactic nematic and conventional nematic mesophases in a sequence with increasing temperature, which were connected by a first-order transition. The analysis of the various features of the small-angle x-ray diffraction patterns indicates that two structural arrangements, namely smectic C-like and conventional nematic structures, coexist inside the cybotactic nematic mesophase of these poly(urethane-ester)s. © 1995 John Wiley & Sons, Inc. 相似文献
13.
Emo Chiellini Andrea Corti Salvatore D'Antone 《Polymer Degradation and Stability》2007,92(7):1378-1383
Several demonstrations of the effective biodegradation in soil of pro-oxidant activated polyethylene (PE) have been reported recently. Nevertheless a comprehensive understanding of the ultimate fate in the environment of the oxidized fragments of oxo-biodegradable polyethylene materials needs the extension of the studies to other natural environments and in particular to aqueous media (river, lake, brackish and marine waters) where accidental plastic littering and the resulting degraded fragments eventually may end up.In this respect, as part of our continuing activity in the area of oxo-biodegradable polymeric materials, in the present paper we wish to report on the results attained in an ongoing investigation on the biodegradation in a water medium of thermally pre-oxidized low density polyethylene (LDPE) film samples containing pro-oxidant additives.Thermally oxidized LDPE-film samples and corresponding acetone extractable fractions were submitted to the effect of microorganism flora present in river water. The effective biodegradation was assessed by monitoring the amount of CO2 developed over time in a respirometer apparatus. Levels of biodegradation up to 12 and 48% for the degraded fragments and corresponding fractions extracted with boiling acetone were detected on a 100-day time frame. 相似文献
14.
Oriano Francescangeli Bin Yang Emo Chiellini Giancarlo Galli Annino Sante Angeloni Michele Laus 《Liquid crystals》1993,14(4):981-990
An X-ray study is performed on powder specimens and on stretched oriented fibres of two liquid crystalline polyacrylates containing the azobenzene mesogenic unit with either a 4'-n-pentyloxy (sample 1-4) or 4'-n-hexyloxy (sample 1-5) substituent. The X-ray diffraction patterns of both samples showed the presence of a bilayer smectic C mesophase with the mesogneic groups tilted by an angle β ∼ 45° (1-4) or β ∼ 38° (1-5) with respect to the layer normal. The electron density profile p(z) along the direction normal to the smectic layers was calculated by Fourier inversion and possible structural models of the smectic mesophase are discussed. A partial interdigitation of the terminal alkyloxy substituents appears to occur. 相似文献
15.
Emo Welzl 《Journal of Combinatorial Theory, Series B》1984,37(3):235-244
The mechanism of interpretation (subgraph homomorphism, homomorphic embedding, general coloring) gives rise to a “geography” of graphs. The position of symmetric graphs in this geography is investigated. 相似文献
16.
17.
Vera L. Covolan Roberta Di Ponzio Federica Chiellini Elizabeth Grillo Fernandes Roberto Solaro Emo Chiellini 《Macromolecular Symposia》2004,218(1):273-282
Polyurethanes (PUs) composed by hard and soft segments have been extensively used in the manufacturing of biocompatible prosthesis and medical devices. A broad variety of PUs can be obtained by modifying the balance between both segments. In the present work, different basically-flexible PUs have been prepared by employing different combinations of aliphatic hexamethylene diisocyanate, poly(ethylene glycol) (Mw 400 Da), poly(ϵ-caprolactone) diol (Mw 530 Da), and 1,4-butanediol. Thermal analysis of the synthesized PUs demonstrated high thermal stability and the assumption of glassy state well below room temperature, in agreement with their marked flexibility. Morphological characterization of PUs films indicated that films prepared by spin coating were smoother and more homogeneous than those obtained by casting. Biological assays performed by using 3T3/BALB-C mouse embryo fibroblast cell line confirmed the absence of toxicity and hence the biocompatibility of PU-films. 相似文献
18.
Let M be a random (n×n)-matrix over GF[q] such that for each entry Mij in M and for each nonzero field element α the probability Pr[Mij=α] is p/(q−1), where p=(log n−c)/n and c is an arbitrary but fixed positive constant. The probability for a matrix entry to be zero is 1−p. It is shown that the expected rank of M is n−𝒪(1). Furthermore, there is a constant A such that the probability that the rank is less than n−k is less than A/qk. It is also shown that if c grows depending on n and is unbounded as n goes to infinity, then the expected difference between the rank of M and n is unbounded. © 1997 John Wiley & Sons, Inc. Random Struct. Alg., 10 , 407–419, 1997 相似文献
19.
Emo Chiellini Patrizia Cinelli Vassilka I. Ilieva Antonio Ceccanti Pavol Alexy Dusan Bakos 《Macromolecular Symposia》2003,197(1):125-132
Hybrid blends of poly(vinyl alcohol) (PVA) and collagen hydrolyzate (CH), an added value waste from leather indutry, have been converted by blown molding extrusion, to environmentally degradable films. Blown extruded films comprising 5-15% of CH, were tested as sel fertilizing mulching films and analyzed for their propensity to enviromental degradation. PVA/CH films rapidly disintegrate when buried in soil, and resulted promising for application such as transplanting films, with additional fertilizing action of CH. 相似文献
20.
Francesca Signori Roberto Solaro Emo Chiellini Priscilla A.M. Lips Pieter J. Dijkstra Jan Feijen 《Macromolecular Symposia》2003,197(1):289-302
The present work was aimed at the development of functional polymeric materials to be used in the targeted delivery of proteic drug and tissue engineering fields. The adopted strategy was based on the design of special polymer classes whose structures and functionality could be easily modified by finely tuned synthetic procedures. Poly(ether ester)s containing H-bonding units were chosen as promising materials for the proposed applications. Commercially available precursors were successfully used for the synthesis of symmetrical diesters containing different H-bonding groups (amide, carbamate, and urea moieties). In all cases, pure products were obtained in good yields. Bulk polycondensation of the monomeric precursors with different mixtures of 1,4-butanediol and PEG 1000 diol afforded a variety of high molecular weight polymeric structures. Physical-chemical characterization of the polymers indicates that their thermal, mechanical, and swelling properties can be tailored by a proper selection of the H-bonding group and of the composition of the feed mixture. 相似文献