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排序方式: 共有9058条查询结果,搜索用时 15 毫秒
51.
52.
In order to extend the expressive power of deductive databases, a formula that can have existential quantifiers in prenex normal form in a restricted way is defined as an extended rule. With the extended rule, we can easily define a virtual view that requires a division operation of relational algebra to evaluate. The paper addresses a recursive query evaluation where at least one formula in a recursive rule set is of an extended rule. We investigate transformable recursions as well as four cases of non-transformable recursions of transitive-closure-like and linear type. The work reveals that occurrence of an existentially quantified variable in the extended recursive body predicate might dramatically limit the level of recursive search. In particular, the number of iterations to answer extended queries can be determined, independently of database contents 相似文献
53.
Young -Wook Kim Jin -Soo Song Sang -Whan Park June -Gunn Lee 《Journal of Materials Science》1993,28(14):3866-3868
A new, faster process was developed for the fabrication of Nicalon-fibre-reinforced SiC composites by combining polymer solution infiltration (PSI) and chemical vapour infiltration (CVI). The process led to the near-net-shape fabrication of fibre-reinforced ceramic-matrix composites and reduced infiltration time. Typical flexural strength and fracture toughness of these composites were 296 MPa and 10.9 MPa m1/2 at room temperature (RT) and 252 MPa and 9.6 MPa m1/2 at 1000 °C, respectively. The composites exhibited load-carrying capability after crack initiation. 相似文献
54.
对长石、石英、龙岩土、莱阳土4种因素各取4个水平,用正交表L16(45)安排16个试验,分析了这16个试验产品的吸水率、白度、热稳定性与每种因素各水平之间的关系.得出了白瓷坯料的最佳配方。其中,长石19,石英21,龙岩土21.莱阳土0. 相似文献
55.
OE Santana Rodríguez ML Malé Gil JF HernándezSantana JM Limi?ana Ca?al AM Martín Sánchez 《Canadian Metallurgical Quarterly》1998,14(6):555-561
Von Hippel-Lindau disease (VHL) is an autosomal dominant tumour syndrome caused by germline mutations of the VHL tumour suppressor gene located on chromosome 3p25-26. In VHL tumours may occur in 14 different target organs, including the eye. Retinal angiomas are considered the first manifestation of VHL disease in 43% of cases, and the cumulative probability of developing a retinal angioma in one or both eyes rises during each decade of life, reaching 80% for patients over 80 years old. Since 1976 patients with VHL at the University Hospital of Utrecht and their at-risk relatives have been screened periodically by a multidisciplinary team. Long-term follow-up ophthalmological data were analysed with special attention to natural course and results of treatment. In addition, we looked for a genotype-phenotype correlation. Retinal angiomas were found in all families. In one large family with a missense mutation (V170D) of the VHL gene, in which the complete spectrum of visceral- and central nervous system (CNS) features of VHL is present, macular, parapapillary, optic disc and ora serrata angiomas were also found. In general, however, a clear-cut genotype-phenotype correlation could not be found. Only early detection and treatment of peripheral retinal angiomas can be expected to decrease the percentage of patients with decreased visual acuity. Therefore, early detection and treatment of these tumours is of paramount importance. Ophthalmological screening of patients and persons at risk should start as early as possible. In patients with apparently sporadic retinal angiomas it is advisable to perform germline DNA analysis, since the risk of developing VHL is high, especially if the angiomas are bilateral, or unilateral and multifocal, if the patient is young, or if there is a family history suggestive of VHL. 相似文献
56.
57.
X Calvet M Navarro M Gil A Lafont I Sanfeliu E Brullet R Campo B Dalmau E Rivero P Mas 《Canadian Metallurgical Quarterly》1998,93(12):2501-2507
OBJECTIVE: The aim of this study was to investigate the clinical and epidemiological factors associated with the appearance of peptic ulcer in patients with cirrhosis and, in particular, the role of Helicobacter pylori infection. METHODS: A total of 201 of 220 consecutive patients included in a prospective study that aimed to evaluate the effect of dietary intervention on cirrhotic complications and survival underwent upper gastrointestinal endoscopy. At entry, an epidemiological and clinical questionnaire was completed and the presence of peptic ulcer disease or esophageal varices at endoscopy was prospectively collected. Sera were obtained and stored at -70 degrees C until analyzed, being tested afterward for Helicobacter pylori antibodies using a commercial ELISA kit. RESULTS: Eleven of 201 patients had borderline anti-Helicobacter pylori IgG titers and were excluded from further analysis. In the remaining 190 patients, point prevalence of peptic ulcer was 10.5% and lifetime prevalence 24.7%. Multivariate analysis selected male sex (OR 2.3; 95%CI 1.09-4.89) and Helicobacter pylori seropositivity (OR: 1.7, 95%CI 1.02-2.81) as the variables independently related to peptic ulcer disease. CONCLUSIONS: Male sex and seropositivity for Helicobacter pylori are the major risk factors for peptic ulcer in cirrhosis. 相似文献
58.
Jung Nam Bae Jin Young Kim Geon Kim Yong Tae Lee Jae Sang Cha 《Multimedia Tools and Applications》2012,57(2):359-372
Recently, watermarking based data transmission techniques using terrestrial digital TV signal have been proposed since they
are also cost-free and can overcome the limitations of GPS. However, in the previous watermarking based methods, the detection
accuracy is low and additional data rate is too low. Thus, we propose the throughput enhancement method by employing the TZCD-MBOK
watermarking technique in T-DMB system. By applying the proposed scheme to T-DMB, it allows additional data transmission for
disaster broadcasting and improves efficiency of data transmission in shadow region and indoor to mobile environment through
watermarking spread code. From the simulation results, we confirm the proposed watermarking scheme affected on the existing
T-DMB signal. Moreover, it was also confirmed that the system capacity increases as the power of additional watermarking signal
rose. The results of the paper can be applied to wireless multimedia digital broadcasting systems. 相似文献
59.
Due to the explosive increases of data from both the cyber and physical worlds, the demand for database support in embedded systems is increasing. Databases for embedded systems, or embedded databases, are expected to provide timely in situ data services under various resource constraints, such as limited energy. However, traditional buffer cache management schemes, in which the primary goal is to minimize the number of I/O operations, is problematic since they do not consider the constraints of modern embedded devices such as limited energy and distinctive underlying storage. In particular, due to asymmetric read/write characteristics of flash memory-based storage of modern embedded devices, minimum buffer cache misses neither coincide with minimum power consumption nor minimum I/O deadline misses. In this paper we propose a novel power- and time-aware buffer cache management scheme for embedded databases. A novel multi-dimensional feedback control architecture is proposed and the characteristics of underlying storage of modern embedded devices is exploited for the simultaneous support of the desired I/O power consumption and the I/O deadline miss ratio. We have shown through an extensive simulation that our approach satisfies both power and timing requirements in I/O operations under a variety of workloads while consuming significantly smaller buffer space than baseline approaches. 相似文献
60.
Jeong Won Kim Hee Won Kang Dong-Hwan Hwang Sang Jeong Lee 《International Journal of Control, Automation and Systems》2012,10(3):529-535
A signal tracking method of GNSS receivers for spinning vehicles is proposed in order to eliminate the influence of spinning to the GNSS signal of a vehicle. In the proposed method, a rotation tracking loop is added into the carrier tracking loop of a conventional GNSS receiver. The proposed method was verified through computer simulations and an experiment for live GPS signals. The results show that the proposed method gives an accurate tracking performance. 相似文献