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1.
In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the hydrodynamic force is the main force because the blades are feathered to reduce the lifting force. The first-order hydrodynamic forces are calculated by WADAM, while the second-order wave forces are calculated by a customized MATLAB module. Then the hydrodynamic coefficients are transferred to the wind turbine analytical code FAST. Through the comparisons of dynamic responses between the first- and second-order numerical models, it is found that the second-order wave forces significantly influence the motion of floating wind turbine under the survival condition. Moreover, neglecting the second-order force significantly underestimates the tension forces in the mooring lines.  相似文献   

2.
While haptics (simulated touch) represents a potential breakthrough technology for science teaching and learning, there is relatively little research into its differential impact in the context of teaching and learning. This paper describes the testing of a haptically enhanced simulation (HES) for learning about buoyancy. Despite a lifetime of everyday experiences, a scientifically sound explanation of buoyancy remains difficult to construct for many. It requires the integration of domain-specific knowledge regarding density, fluid, force, gravity, mass, weight, and buoyancy. Prior studies suggest that novices often focus on only one dimension of the sinking and floating phenomenon. Our HES was designed to promote the integration of the subconcepts of density and buoyant forces and stresses the relationship between the object itself and the surrounding fluid. The study employed a randomized pretest–posttest control group research design and a suite of measures including an open-ended prompt and objective content questions to provide insights into the influence of haptic feedback on undergraduate students’ thinking about buoyancy. A convenience sample (n = 40) was drawn from a university’s population of undergraduate elementary education majors. Two groups were formed from haptic feedback (n = 22) and no haptic feedback (n = 18). Through content analysis, discernible differences were seen in the posttest explanations sinking and floating across treatment groups. Learners that experienced the haptic feedback made more frequent use of “haptically grounded” terms (e.g., mass, gravity, buoyant force, pushing), leading us to begin to build a local theory of language-mediated haptic cognition.  相似文献   

3.
A novel floating foundation to support the NREL offshore 5 MW wind turbine was designed conceptually by combining the characteristics of barge and Spar. The main focus was structural design and hydrodynamic modelling. Based on this novel floating foundation, the hydrodynamic performance was investigated in the frequency domain and time domain by using the wave analysis software HydroD and DeepC from Det Norske Veritas. The frequency domain analysis was conducted to investigate the effects of the incident wave angle and water depth. The time-domain analysis was carried out to evaluate the response of the floating foundation under a selected operational condition. The hydrodynamic performances of this floating foundation with respect to time series and response spectra were also investigated in this study.  相似文献   

4.
This article examines the main strands of thinking about gravity through the ages and the continuity of thought-experiments, from the early Greeks, through medieval times, to Galileo, Newton and Einstein. The key ideas are used to contextualise an empirical study of 247 children’s ideas about falling objects carried out in China and New Zealand, including the use of scenarios involving thrown and dropped items, and objects falling down deep well holes (as in Carroll’s Alice in Wonderland). The sample included 68 pre-school pupils, 68 primary school pupils, 56 middle school students, and 55 high school students; with approximately equal numbers in each group and of boys and girls in each group in each culture. The methodology utilised Piagetian interviews with three media (verbal language, drawing, and play-dough), a shadow stick; and everyday items including model people and soft model animals. The data from each group was categorised and analysed with Kolmogorov–Smirnov Two-Sample Tests and Spearman r s coefficients. It was hypothesised and confirmed (at K–S alpha levels .05; r s : p < .001) that cross-age and cross-cultural research and analysis would reveal that (a) an intuitive sense of gravity is present from an early age and develops in association with concepts like Earth shape and motion; (b) the development of concepts of gravity is similar in cultures such as China and New Zealand where teachers hold a scientific world view; and (c) children’s concepts of Earth motion, Earth shape, and gravity are coherent rather than fragmented. It was also demonstrated that multi-media interviews together with concrete experiences and thought-experiments afforded children the opportunity to share their emerging concepts of gravity. The findings provide information that teachers might use for lessons at an appropriate level.  相似文献   

5.
The parameters obtained from oedometric consolidation tests are commonly used in the development of constitutive modeling and for engineering practice. This paper focuses on the influence of the natural deposition plane orientation on oe- dometric consolidation behavior of three natural clays from the southeast coast of China. Oedometer tests were conducted on intact specimens prepared by sampling at a series of angles relative to the natural deposition plane. For each specimen, yield stress, compressibility indexes, secondary compression, and permeability coefficients were determined. The influence of the sampling angle on these properties was investigated, revealing that yield stress, compression index, swelling index, creep index, ratio of secondary compression coefficient to compression index （Cae/JCc） and permeability coefficient were all dependent to some extent on the sampling angle. These findings indicate the role of the anisotropy due to the natural deposition on the oedometric con- solidation behavior.  相似文献   

6.
Ritavan 《Resonance》2014,19(5):466-470
Taylor’s theorem in analysis provides a way of approximating an n+1-times differentiable real function by an nth degree polynomial in a neighbourhood of a point x 0. The usefulness of the theorem lies in the fact that if the bounds on |f (n+1)(x)| are known, then the error introduced by the polynomial approximation can be estimated. So while Taylor’s theorem provides an extremely useful manner of approximating the given function to a desired degree of precision in a neighbourhood of a given point, it says nothing about the nature of the polynomial approximation itself, and intuitive arguments are often offered to explain why the derivatives of f must figure in the coefficients of such a polynomial. In what follows, we shall attempt a rigorous explanation of the sense in which such a polynomial is the ‘best’ approximation of the given function.  相似文献   

7.
Within-student dynamics in perceptions of instructional quality have been neglected, although student states constitute a major share of these perceptions. The present study examined the structure and correlates of student state perceptions of the three basic dimensions, teacher support, cognitive activation, and classroom management. We conducted a three-week experience sampling study using state measures in four subjects (observations: nmathematics = 2,681, nphysics = 1,555, nGerman = 2,026, nEnglish = 1,835) and analyzed data from 372 German secondary school students (Mage = 15.3 years), conducting two-level confirmatory factor analyses. Against more parsimonious solutions, the postulated three-factor structure was confirmed within- and between-students across subjects, entailing 51% within-student variance on average. Similar to trait-like perceptions, state perceptions were positively related to grades and academic interest. Our results support the factorial and convergent validity of state student perceptions of instructional quality, expanding upon between-person-based literature and uncovering opportunities to enhance teaching effectiveness.  相似文献   

8.
N-valeronitrile-N’-methylimidazolium hexafluorophosphate ([C 4 CNmim]+ PF 6),as a novel ionic liquid with polar nitrile functional group,was prepared.The structure of the ionic liquid was characterized by using IR and 1 H NMR.As a medium,the ionic liquid plays an important role in copolymerization of carbon monoxide (CO) with styrene (St).Some synthetic conditions were determined,including the usage of ionic liquid,palladium composite catalyst and methanol,CO pressure,reaction time and reaction temperature.The influence of these factors on catalytic activity was analyzed.The results show that the catalytic activity has reached 1 724.1 gStCO/(gPd·h) and the catalyst could be reused 5 times under the optimal condition:composite catalyst 0.015 mmol,ionic liquid 3 mL,methanol 0.75 mL,CO pressure 2MPa,reaction time 2 h and reaction temperature 70℃.This CO/St copolymerization within [C 4 CNmim]+ PF 6 system could facilitate ionic liquids with efficient and economical applications to polymeric materials.  相似文献   

9.
Conventional consolidation tests on reconstituted specimens of numerous natural soft clays show a decreasing of creep index Cae with increasing soil density. Based on all selected and conducted experimental results, a modified creep index Cae＊ defined in double logarithmic plane lge-lgt, was plotted for various clays, from which Cae＊ can be assumed as a constant for different soil densities. Then, the modified creep index was applied to a newly developed elastic viscoplastic model. In this way, the modified creep index Ca＊ can naturally take into account the nonlinear Cae revealing the influence of soil density in the soil assemblies without additional parameters. Finally, the enhanced model was incorporated into the finite element code ABAQUS and used to simulate a consolidation test and a test embankment. The improvement of simulations by the modified creep index was highlighted by comparing simulations using the conventional creep index Cae.  相似文献   

10.
INTRODUCTION Steel rebar embedded in concrete is protectedagainst corrosion by the thin passive film on its sur-face and the physical protection from concrete. Thealkaline environment (pH≥12.5) of the concrete poresolution triggers passivation on the rebar surface andformation of the protective oxide film. The physicaprotection of concrete coverage hinders the invasionof aggressive agents. However, this passivity can bebroken down by local pH loss as a result of concretecracking or the…  相似文献   

11.
The stabilizing conditions of W/O microemulsion of Tx-6-C4H9OH/c-C6h12/H2O system were studied by visual observation.The result shows that when the weight ratio of Tx-6 to C4H9OH is 4:1 ,the W/O microemulsion system has stabilizing and extensive regions,and the system is insensitive to the values of pH and in the range of room temperature.In accordance with the theoretical value of HLB,the suitable value of HLB for Tx-6 and C4H9OH to compose microemulsion is greater than 9,less than or equal to 10 value of HLB.the suitable value of HLB for Tx-6 and C4H9OH to compose microemulsion is greater than 9,less than or equal to 10.  相似文献   

12.
1　Introduction　AmatrixA∈Cn×missaidtobecentrohermitianifA =Jn AJm,andskewcentrohermitianifA =-Jn AJm,where Adenotetheconjugateofthema trixAandJlisthepermutationmatrixoforderlwithonesonthecrossdiagonal(bottomlefttotopright)andzeroselsewhere .ThehermitianToeplitzmatricesformanimportantsubclassofcentrohermi tianmatriceswhichoccurnaturallyindigitalsignalprocessingandotherareas ,seeforinstance[1] andreferencetherein .Thecentrohermitianandrelatedmatricesrecentlyplayanimportantroleinthesolu…  相似文献   

13.
In this paper, we are interested in the following general question: Given a module Mwhich has finite hollow dimension and which has a finite collection of submodules Ki (1≤i≤n) such that M=K1 ... Kn, can we find an expression for the hollow dimension of Min terms of hollow dimensions of modules built up in some way from K1 Kn? We prove the following theorem:Let Mbe an amply supplemented module having finite hollow dimension and let Ki (1≤i≤n) be a finite collection of submodules of Msuch that M=K1 ... Kn. Then the hollow dimension h(M) of Mis the sum of the hollow dimensions of Ki (1≤i≤n) ifand only if Ki is a supplement of K1 ... Ki-1 Ki 1 ... Kn in Mfor each 1≤i≤n.  相似文献   

14.
冰片在中风及假手术大鼠体内的药代动力学研究(英文)简   总被引：1，自引：0，他引：1  
Objective： This study was designed to investigate the pharmacokinetics of borneol in the pathological conditions of stroke and evaluate the pharmacokinetic differences of borneol caused by stroke after oral administration of borneol and Xingnaojing （XNJ）. Methods： The rats were divided into two groups, ischemia-reperfusion （IR） and sham-operated （SO） rats. Each group contained two subgroups： pure borneol and XNJ subgroups. After administration with the same dosages of borneol 162.0 mg/kg, plasma samples were collected. The cerebral ischemia-reperfusion model was created by reversible middle cerebral artery occlusion （MCAO）. The blood samples were collected punc- tually after oral administration and a specific gas chromatographic system-flame ionization detector （GC-FID） method was developed and employed to determine the level of borneol in the plasma. The pharmacokinetic parameters were analyzed using non-compartmental methods with Kinetica. Results： After administration of borneol, the maximum plasma concentration （Cmax） and area under the curve （AUC） values in stroke rats significantly increased by 302% and 275%, respectively, compared with the SO rats, and the same phenomenon appeared after administration of XNJ. In the rats with the same physiological conditions, the Cmax and AUC had higher values in the borneol subgroup （P〈0.05）. Conclusions： These results suggest that the pathological damages of ischemia-reperfusion have a significant impact on the pharmacokinetic traits of borneol and that there are some components in XNJ inhibiting the absorption of borneol.  相似文献   

15.
Objective: The intoxications caused by 2,4-dinitrophenol (2,4-DNP), even death, have been frequently reported in recent years. This study aims to investigate the dynamic changes of plasma toxin concentration and explore the clinical value of resin hemoperfusion (HP) in the treatment of patients with acute 2,4-DNP poisoning. Methods: We reported 16 cases of acute 2,4-DNP poisoning through occupational exposure due to ignoring the risk of poisoning. The blood samples were collected from the 14 survivors. According to the different treatments of resin HP, the survivors were divided into routine HP (n=5) and intensive HP (n=9) groups. Ultra high performance liquid chromatography/tandem mass spectroscopy (UPLC-MS/MS) was used to detect the 2,4-DNP concentration in plasma in this study. Results: The 14 survivors recovered very well after treatment. The initial plasma 2,4-DNP concentrations (C 1) of survivors ranged from 0.25 to 41.88 µg/ml (mean (12.56±13.93) µg/ml). A positive correlation existed between initial plasma 2,4-DNP concentration (C 1) and temperature. The elimination of 2,4-DNP was slow and persistent, and the total clearance rates of plasma toxin from the 1st to 3rd day (R 3), the 3rd to 7th day (R 3–7), and the 1st to 7th day (R 7), were only (53.03±14.04)%, (55.25±10.50)%, and (78.29±10.22)%, respectively. The plasma toxin was cleared up to 25 d after poisoning in most of the patients. The R 3, R 3–7, and R 7 in the intensive HP group were all apparently higher than those in the routine HP group, with statistical significance (P<0.05). Simultaneously, the elimination half-life (t 1/2) of 2,4-DNP in the intensive HP group was apparently shorter than that in the routine HP group, with statistical significance (P<0.05). Conclusions: The clinicians should be aware of this slow and persistent process in the elimination of plasma 2,4-DNP. Higher initial plasma toxin concentration resulted in a more severe fever for the patient. According to the limited data, longer and more frequent resin HP may accelerate to eliminate the poison.  相似文献   

16.
Selecting a subset of predictors from a pool of potential predictors continues to be a common problem encountered by applied researchers in education. Because of several limitations associated with stepwise variable selection procedures, the examination of all possible regression solutions has been recommended. The authors evaluated the use of Mallow's Cp and Wherry's adjusted R 2 statistics to select a final model from a pool of model solutions. Neither the Cp nor the adjusted R 2 statistic correctly identified the underlying regression model any better and was generally worse than the stepwise selection method, which itself was poor. Using any of the model selection procedures studied here resulted in biased estimates of the authentic regression coefficients and underestimation of their standard errors. The use of theory and professional judgment is recommended for the selection of variables in a prediction equation.  相似文献   

17.
The copolymerization of CO and styrene catalyzed by Pd/C toward the formation of polyketones(PK)was studied in the N-valeronitrile-N'-methylimidazolium hexafluorophosphate([C4CNmim]+PF-6) medium. The synthesized PK was characterized by Fourier transform infrared(FTIR), elemental analysis, 13C-nuclear magnetic resonance(13C-NMR), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and gel permeation chromatography(GPC). The supported ionic liquid film on the surface of Pd/C catalyst can prevent the products from covering the hole of active carbon due to its chemical stability and weak coordination ability with metal ions, and thus efficiently improve the catalytic activity. The effects of different amounts of ionic liquid on the catalytic activity and reusability of the catalyst and the molecular weight of PK were discussed. When the usage of ionic liquid is 10wt%(0.1 g ionic liquid / 1 g active carbon carrier) and the theoretical content of Pd2+ is 5wt%(0.05 g Pd2+/ 1 g active carbon carrier), the highest catalytic activity 2 963.64 gSTCO/(gPd·h) is achieved with the molecular weight and polydispersity index of PK as Mn=9 684, Mw=13 452 and Mw /Mn=1.389.  相似文献   

18.
Transitive inference is the ability, given thatA >B andB >C, to infer thatA >C. Pigeons, rats, chimpanzees, squirrel monkeys, and humans as young as 4 years have all been shown capable of this. In this paper, simple associative learning models are explored as accounts of nonverbal transitive inference performance. A Bush-Mosteller-based model can account for transitive inference under limited conditions. A Rescorla-Wagner-based model can account for transitive inference under all conditions in the literature, but cannot account for some additional nontransitive tests. A final configural model can also account for these nontransitive data. The ability of this model to account for transitive inference formation in humans is also considered.  相似文献   

19.
本文运用刚体运动学原理及集中质量方法,建立了单体和双体深水网箱在波浪作用下的数学模型,并利用物理模型试验结果对数学模型进行验证。在此基础上,比较了单体网箱和双体网箱的水动力特性。由数值模拟结果可知,在相同波况条件下,双体网箱各类锚绳受力特征值均大于单体网箱对应工况各类锚绳的受力特征值,考虑双体网箱锚绳受力增加情况,其中锚碇锚绳受力平均增幅为65%,连接锚绳受力平均增幅为262.2%,网格锚绳受力平均增幅为95.6%;双体网箱浮架中心点的水平方向运动幅度总体上小于单体网箱对应情况,两种形式网箱的浮架中心点竖直方向运动幅度和倾角大小几乎相等,而两类网箱的网衣体积损失率总体上比较相近。  相似文献   

20.
The study investigates the preschool readiness of moderately preterm children and, in particular, the likely presence of learning disabilities at preschool age. Its theoretical model detects linguistic comprehension and expression; memory-related metacognition and cognition skills; orientation and motor coordination skills; premathematics and preliteracy ones. The research project involved an experimental group made up of 55 moderately preterm children (mean age?=?62 months, mean gestational age?=?34.6 weeks), without any clinical neonatal complications, and low birth weight (M?=?2,100 g, SD?=?350 g); a control group made up of 55 full-term children without pre- and perinatal complications. The children’s primary school reference teachers were given a questionnaire (Observative Questionnaire for Early Identification of Learning Disabilities), which was aimed at identifying any likely social and cognitive skill deficits at preschool age. The data, submitted to nonparametric univariate variance, show how scores of moderately preterm children in the metacognition [U (n1 e?n2?=?55)?=?35, p?=?0.04, r?=?0.49] are statistically lower, other cognitive skills (memory, orientation, and visual–motor coordination) [U (n1?e?n2?=?55)?=?32, p?=?0.02, r?=?0.45], premathematics [U (n1?e?n2?=?55)?=?32, p?=?0.02, r?=?0.44], and the total score [U (n1?e?n2?=?55)?=?31, p?=?0.02, r?=?0.12]. Such data would seem to suggest the need for hypothesizing preventive training and educational paths as a prerequisite for the development of the school abilities.  相似文献   

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