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排序方式: 共有490条查询结果,搜索用时 15 毫秒
1.
In this paper two problems on the class of k -trees, a subclass of the class of chordal graphs, are considered: the fast reordering problem and the isomorphism problem. An O(log 2 n) time parallel algorithm for the fast reordering problem is described that uses O(nk(n-k)/\kern -1ptlog n) processors on a CRCW PRAM proving membership in the class NC for fixed k . An O(nk(k+1)!) time sequential algorithm for the isomorphism problem is obtained representing an improvement over the O(n 2 k(k+1)!) algorithm of Sekharan (the second author) [10]. A parallel version of this sequential algorithm is presented that runs in O(log 2 n) time using O((nk((k+1)!+n-k))/log n) processors improving on a parallel algorithm of Sekharan for the isomorphism problem [10]. Both the sequential and parallel algorithms use a concept introduced in this paper called the kernel of a k -tree. 相似文献
2.
In this paper novel reduced complexity statistical models for the representation of directional wireless channels affected by Rayleigh fading are developed. Their derivation is based on the evaluation of Fourier integrals by means of Gaussian quadrature rules (GQRs). The proposed models represent a communication channel as a tapped-angle and -delay line with non uniform spacing between successive taps. The application of the GQR approach to three different scenarios is also illustrated. Numerical results evidence that these models can provide a simple and accurate stochastic representation of directional fading channels. 相似文献
3.
GP Deriu D Milite F Verlato D Cognolato P Frigatti M Zaramella G Mellone F Greco 《Canadian Metallurgical Quarterly》1998,39(6):729-734
BACKGROUND: The aim of this retrospective study is to analyze the short and long term results of two different surgical treatments in patients with subclavian lesions: common carotid-subclavian artery bypass (CSB) versus transposition of subclavian artery on the common carotid artery (SCT). METHODS: From 1981 until 1995, 40 non randomized patients with symptomatic subclavian steal underwent 20 CSBs and 20 SCTs. Risk factor rates were equally balanced in the two groups. Surgery was carried out routinely under general anesthesia, with electroencephalic continuous monitoring. Patency of revascularization was assessed by physical examination, brachial blood pressure determinations, ultrasound sonography and angiography whenever recurrence of symptoms developed or when the function of repair was in doubt. Patients were examined every year. In Spring 1996 (range 9-189 mos, average 7 years) a general clinical-instrumental follow-up was performed. RESULTS: In the short term (<30 days) mortality was 5%: one death (5%) for pulmonary embolism in a patient with CSB and one for myocardial infarction in a patient with SCT. The early thrombosis rate was 5% (1 CSB and 1 common carotid artery distal to a patent SCT). During follow-up 10 patients (25%) died and 6 were lost. The six-year actuarial patency rate was 100% for SCT and 66% for CSB. Moreover there were 3 thromboses of the vertebral artery homolateral to patent CSBs. CONCLUSIONS: In conclusions SCT should be considered the surgical technical choice for the treatment of proximal subclavian artery lesions. 相似文献
4.
Adaptive Radar Detection of Distributed Targets in Homogeneous and Partially Homogeneous Noise Plus Subspace Interference 总被引:5,自引:0,他引:5
Bandiera F. De Maio A. Greco A.S. Ricci G. 《Signal Processing, IEEE Transactions on》2007,55(4):1223-1237
This paper addresses adaptive radar detection of distributed targets in noise plus interference assumed to belong to a known or unknown subspace of the observables. At the design stage we resort to either the GLRT or the so-called two-step GLRT-based design procedure and assume that a set of noise-only data is available (the so-called secondary data). Detection algorithms have been derived modeling noise vectors, corresponding to different range cells, as independent, zero-mean, complex normal ones, sharing either the same covariance matrix (homogeneous environment) or the same covariance matrix up to possibly different (mean) power levels between primary data, i.e., range cells under test, and secondary ones (partially homogeneous environment). The performance assessment has been conducted by Monte Carlo simulation, also in comparison to previously proposed detection algorithms, and confirms the effectiveness of the newly proposed ones 相似文献
5.
CH Weaver LS Schwartzberg R Birch FA Greco S Rhinehart J Hainsworth T Beeker H Price L Geier J Foster J West B Hazelton CD Buckner 《Canadian Metallurgical Quarterly》1997,37(9):896-903
BACKGROUND: There is great interpatient variability in the number of peripheral blood stem cells collected, as measured by CD34+ cell content, after the administration of chemotherapy and a growth factor. The ability to predict patients who fail to yield adequate quantities of CD34+ cells would be of value. However, very few reports include large numbers of patients treated in an identical fashion. STUDY DESIGN AND METHODS: Between 1991 and 1995, 497 consecutive patients with a variety of malignant diseases received cyclophosphamide (4 g/m2), etoposide (600 mg/m2), and granulocyte-colony-stimulating factor (6 micrograms/kg/day) for mobilization and collection of a target dose > or = 2.5 x 10(8) CD34+ cells per kg. Multivariate analyses were performed to determine the factors associated with failure to achieve this target harvest. RESULTS: A median of 14.71 x 10(6) CD34+ cells per kg (range, 0.08-137.55) was harvested with a median of 2 (range, 1-11) apheresis procedures. Ninety-one percent of patients yielded > or = 2.5 x 10(5) CD34+ cells per kg. Patients with Stage II-III breast cancer, who had pretreatment platelet counts > or = 150 x 10(9) per L and patients who underwent < or = 1 prior chemotherapy regimen had improved CD34+ cell yields. However, most patients with adverse risk factors yielded > or = 2.5 x 10(6) CD34+ cells per kg. CONCLUSION: A regimen of cyclophosphamide, etoposide, and granulocyte-colony-stimulating factor led to the successful collection of adequate numbers of CD34+ cells in most patients without excessive toxicity. These observations confirm previous reports that intense prior therapy adversely affects the quantity of CD34+ cells harvested. Pretreatment and posttreatment variables did not predict with any certainty the small fraction of patients who fail to yield > or = 2.5 x 10(6) CD34+ cells per kg via multiple apheresis procedures. 相似文献
6.
The influence of the addition of two ethylene-propylene random copolymers (EPM) with different composition on the mechanical properties, thermal behavior and overall morphology of high density polyethylene (HDPE)/isotactic polypropylene (iPP) blends, was investigated on extruded samples. The experimental data showed that the morphology of binary HDPE/iPP blends is drastically modified by these additives and that the ultimate mechanical properties of these mixtures are greatly improved. A reasonable explanation of these results can be ascribed to the fact that these copolymers can act as “compatibilizing agents” in the amorphous regions of the two semicrystalline homopolymers. The extent of such effects is dependent on the chemical structure and/or on the molecular mass of the added copolymer as well as on the HDPE/iPP blend compositions. 相似文献
7.
Binary and m-ary encoding in applications of tree-based genetic algorithms for QoS routing 总被引:1,自引:1,他引:0
Vincenzo Maniscalco Silvana Greco Polito Antonio Intagliata 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2014,18(9):1705-1714
Ubiquitous and Pervasive Computing (UPC) applications often have Quality of Service (QoS) requirements. These become constraints for the UPC network infrastructure. In this paper, we refer to Mobile ad Hoc Networks, one of the most important technologies supporting UPC, and investigate on Genetic Algorithms (GAs) for QoS routing. GAs are part of the soft computing paradigm and can solve the NP search of QoS routes with multiple constraints. We elaborate on tree-based GAs, which represent the set of paths from source to destination as a tree and encode them through the crossed junctions. While their most well-known applications use m-ary encoding representing single paths in the chromosomes, in this paper we discuss a binary encoding with the objective of improving the convergence speed. The binary encoding represents classes of paths in the chromosomes and allows local search on classes of paths. These classes are both collectively exhaustive and mutually exclusive. Simulation results compare convergence speed and scalability of GA applications with binary and m-ary encoding in networks with an increasing number of nodes and links per node. As the per-class processing is reason of additional computational cost, an hybrid GA application that uses both binary and m-ary encoding is introduced. 相似文献
8.
L. D'Orazio R. Greco C. Mancarella E. Martuscelli G. Ragosta C. Silvesrte 《Polymer Engineering and Science》1982,22(9):536-544
Two random commercial ethylene-propylene copolymers (EPM) with different ethylene content have been added to binary isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends by melt mixing in a Brabender-like apparatus. Impact Izod tests and a morphological analysis on the fractured surfaces of broken specimens have been performed and discussed, in order to improve the deficiency in toughness of the binary HDPE/iPP mixtures. The results show that the impact performance of both homopolymers and HDPE/iPP binary blends is strongly improved by the addition of the EPM copolymers. Such an effect is related to the fact that the overall morphology, as well as the mechanism and mode of fracture, are greatly modified by the presence of such additives. The extent is dependent on factors such as the nature of the matrix (HDPE or iPP), the composition, and the chemical structure and/or the molecular mass of the added copolymer. 相似文献
9.
Abstract. In this paper two problems on the class of k -trees, a subclass of the class of chordal graphs, are considered: the fast reordering problem and the isomorphism problem. An O(log
2
n) time parallel algorithm for the fast reordering problem is described that uses O(nk(n-k)/\kern -1ptlog n) processors on a CRCW PRAM proving membership in the class NC for fixed k . An O(nk(k+1)!) time sequential algorithm for the isomorphism problem is obtained representing an improvement over the O(n
2
k(k+1)!) algorithm of Sekharan (the second author) [10]. A parallel version of this sequential algorithm is presented that runs in
O(log
2
n) time using O((nk((k+1)!+n-k))/log n) processors improving on a parallel algorithm of Sekharan for the isomorphism problem [10]. Both the sequential and parallel
algorithms use a concept introduced in this paper called the kernel of a k -tree. 相似文献
10.
Some sources of error with multiphase homodyne interferometry are reviewed. A major advantage over the classic two-channel approach is that the inaccuracies that originate from laser-power fluctuations and drifts are shown to be automatically compensated for by proper adjustment of the light beams. 相似文献