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排序方式: 共有527条查询结果,搜索用时 842 毫秒
1.
The stress-whitened damage zone that formed ahead of a semicircular notch during slow tensile loading has been measured from
optical micrographs of translucent blends of poly(vinyl chloride) (PVC) with experimental chlorinated polyethylene (CPE) resins.
When the zone was small, the plane strain condition applied and from the elastic stress distribution a constant mean stress
condition was found at the boundary of the crescent-shaped zone. The critical mean stress did not depend on the chlorine content
or the chlorine distribution of the experimental CPE resin used in the blend. While the critical mean stress decreased as
the amount of CPE in the blend was increased, the critical volume strain, calculated from the bulk modulus, was independent
of composition and was thought to be the controlling parameter for stress-whitening. When the zone was larger, the shape was
qualitatively described by concepts of stress redistribution in the presence of a plastic zone ahead of the notch. Macroscopic
flow and necking were only detected near the maximum in the stress-displacement curve. 相似文献
2.
3.
A heat balance reaction calorimeter was used to obtain information about the most informative process parameters in polymerizations carried out with Et[Ind]2ZrCl2-methylaluminoxane catalyst. The viscosity of the reaction mixture was found to increase dramatically during the homopolymerization of ethylene, but it could be controlled through appropriate selection of the reaction mixture medium. The mass transfer between the gas and liquid phases was the rate-determining step for the polymerization when the reaction mixture-based Reynolds number was below 2.500. The limited mass transfer between the gas and liquid phases was caused by the intensive activity of the metallocene catalyst and the increased viscosity of the reaction mixture. 相似文献
4.
JL Chiasson R Gomis M Hanefeld RG Josse A Karasik M Laakso 《Canadian Metallurgical Quarterly》1998,21(10):1720-1725
OBJECTIVE: To describe the rationale and design, and to discuss the preliminary screening data, of the Study to Prevent NIDDM (STOP-NIDDM Trial), an international study on the efficacy of the alpha-glucosidase inhibitor acarbose in preventing or delaying the development of type 2 diabetes in a population with impaired glucose tolerance (IGT). RESEARCH DESIGN AND METHODS: A total of 1,418 subjects diagnosed with IGT according to the World Health Organization's criteria and having a fasting plasma glucose concentration > or =5.6 mmol/L were randomized in a double-blind fashion to receive either acarbose (100 mg t.i.d.) or placebo for a predictive median follow-up period of 3.9 years. The primary outcome is the development of type 2 diabetes diagnosed using a 75-g oral glucose tolerance test according to the new criteria. The secondary outcomes are changes in blood pressure, lipid profile, insulin sensitivity, cardiovascular events, and morphometric profile. RESULTS: Screening was performed in a high-risk population. As of 1 March 1997, 4,424 subjects had been screened, and data were available for 3,919 (88.5%) subjects. Of these subjects, 1,200 (30.6%) had glucose intolerance. Of the subjects with glucose intolerance, 521 (13.3%) had previously undetected type 2 diabetes, and 679 (17.3%) had IGT. Of the IGT population, 412 (60.7%) subjects were eligible for the study This population had the following characteristics: the mean age was 54.8 years, 52% of the subjects were female, 53% had more than one risk factor for type 2 diabetes, >90% had a family history of diabetes, 78.2% had a BMI > or =27 kg/m2, 47.5% had high blood pressure, 51.2% had dyslipidemia, and 22.8% of the women had a history of gestational diabetes. CONCLUSIONS: Screening of a high-risk population yields one eligible subject per every 10 volunteers screened. This study should definitely answer the question of whether acarbose can prevent or delay the progression of IGT to type 2 diabetes mellitus. 相似文献
5.
Pekka Manninen Päivi Laakso Heikki Kallio 《Journal of the American Oil Chemists' Society》1995,72(9):1001-1008
This study demonstrates the usefulness of capillary supercritical fluid chromatography (SFC) for the characterization of triacylglycerols
of edible oils and fats. Triacylglycerols were separated according to the acyl carbon number and the degree of unsaturation
on a 25% cyanopropyl/25% phenyl/50% methylpolysiloxane stationary phase. Valuable information concerning the triacylglycerol
composition of berry oils was obtained, despite the overlapping of certain triacylglycerol peaks. Simultaneous analysis of
fat-soluble vitamins and triacylglycerols is not practical by capillary SFC with flame-ionization detection because of the
low concentration of naturally-occurring fat-soluble vitamins in edible oils. Therefore, higher loading of the sample, which
led to overloading of triacylglycerols, was required to get reasonable peaks for fat-soluble vitamins. The method was applied
to the characterization of triacylglycerols and tocopherols in sea buckthorn pulp and seed oil, and cloudberry seed oil without
any sample purification prior to SFC. In addition, the stationary phase proved useful for separating the more complex mixtures
of triacylglycerols found in milk fat and in fish oil. 相似文献
6.
Traditional approach to clustering is to fit a model (partition or prototypes) for the given data. We propose a completely opposite approach by fitting the data into a given clustering model that is optimal for similar pathological data of equal size and dimensions. We then perform inverse transform from this pathological data back to the original data while refining the optimal clustering structure during the process. The key idea is that we do not need to find optimal global allocation of the prototypes. Instead, we only need to perform local fine-tuning of the clustering prototypes during the transformation in order to preserve the already optimal clustering structure. 相似文献
7.
Analysis of triacylglycerols by silver-ion high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry 总被引:7,自引:0,他引:7
Triacylglycerols of the seed oils rich in α- and/or γ-linolenic acid moieties were separated by silver-ion high-performance
liquid chromatography (HPLC) followed by on-line atmospheric pressure chemical ionization-mass spectrometric (APCI-MS) detection.
Mass spectra of most triacylglycerols exhibited abundant [M + H]+ and [M − RCO2]+ ions, which defined the molecular weight and the molecular association of fatty acyl residues of a triacylglycerol, respectively.
Silver ions formed weaker complexes with triacylglycerols containing γ-linolenic acid than with those containing α-linolenic
acid, i.e., the elution order of molecules wasXYT
γ>XYT
α’,XT
γ
T
α>XT
α
T
α>, andT
γ
T
γ
T
γ>T
γ
T
γ
T
α>T
γ
T
α
T
α>T
α
T
α
T
α, whereT
α=α-linolenic acid,T
γ=γ-linolenic acid, andX, Y=fatty acids different from linolenic acid. Furthermore, silver-ion HPLC resulted in partial separation within equally unsaturated
triacylglycerols according to differences in the combined number of acyl carbons. Regioisomeric forms of triacylglycerols
were not determined from the seed oil samples, although differences were measured with reference compounds in the relative
abundances of [M − RCO2]+ ions formed by a loss of a fatty acyl residue from thesn-2 position and thesn-1/3 positions. Silverion HPLC/APCI-MS provided valuable information for structure elucidation of seed oil triacylglycerols:
43 molecular species were identified from cloudberry seed oil, 39 from evening primrose oil, 79 from borage oil, 44 from alpine
currant, and 56 from black currant seed oils. The quantitation requires to be studied further, especially in those cases where
several molecular weight species of triacylglycerols eluted in a single chromatographic peak. 相似文献
8.
Mikko Nuutinen Toni Virtanen Tuomas Leisti Terhi Mustonen Jenni Radun Jukka Häkkinen 《Multimedia Tools and Applications》2016,75(4):2367-2391
The Dynamic Reference (DR) method has been developed for subjective image quality experiments in which original or undistorted images are unavailable. The DR method creates reference image series from test images. Reference images are presented to observers as a slide show prior to evaluating their quality. As the observers view the set of reference images, they determine the overall variation in quality within the set of test images. This study compared the performance of the DR method to that of the standardized absolute category rating (ACR) and paired comparison (PC) methods. We measured the performance of each method in terms of time effort and discriminability. The results showed that the DR method is faster than the PC method and more accurate than the ACR method. The DR method is especially suitable for experiments that require highly accurate results in a short time. 相似文献
9.
10.
Heikki Srkel Jari Takatalo Patrick May Mikko Laakso Gte Nyman 《International journal of human-computer studies》2009,67(9):787-799
Human movement in virtual environments (VEs) is a largely unstudied area, and there are no well-established methods of measuring it in VEs. Consequently, it is unclear how movement affects the experiential side of VEs. We introduce a novel method of measuring and modelling human movement. A specific information entropy-based modelling method enabled us to identify different movement patterns and analyse the experiential components related to them. The data was collected by registering the movement patterns of 68 participants who were in a virtual house doing a search task. The experiential side of the VE was measured with the Experimental Virtual Environment Questionnaire (EVEQ). Four movement patterns were identified. In addition, fluent movement in VEs was related to a high sense of presence. Moreover, the participants who moved fluently in the environment assessed their skills high. The results show how movement is related the way in which people experience the VE. The movement analysis method introduced here is applicable to other related research areas as well. 相似文献