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1.
Suppose {Xi,i≥1} and {Yi, i≥1} are two independent sequences with distribution functions and , respectively. Zi,n is the combination of Xi and Yi with a probability for each I with 1≤ i≤n. The extreme value distribution GZ(x) of this particular triangular array of the i.i.d. Random variables Z1,n,… Z2,n, Zn,n is discussed. We found a new form of the extreme value distributions i)ΦAα1(x)Φα2 and ii) ψAα(x)ψα2(x)α1<α2), which are not max-stable. It occurs if FX and FY belong to the same MDA(Φ) or MDA(Ψ).  相似文献   

2.
The sequences {Zi,n, l≤i≤n}, n≥l have multi-nomial distribution among i.i.d. random variables {X1,i, i≥1}, {X2,i,u≥l }, …, {Xm,i, i≥1 }. The extreme value distribution Gz(x) of this particular triangular array of i.i.d, random variables Z1,n, Z2Zn,n is discussed in this paper. We found a new type of not max-stable extreme value distributions, i) Gz(x) = r-1∏i=1ФAiαi(x) × Фαr (x);ii) Gz (x) = r-1∏i=1ψAiαi (x) × ψαr (x); iii) Gz (x) = r-1∏i=1 ∧Ai (λix) × A(x), r≥2, 0＜α1≤α2≤…≤αr and λi∈ (0,1] for i, l≤i≤r-1 which occur if Fj, …, Fm belong to the same MDA.  相似文献   

3.
In this paper we give a short survey on a problem on extremal quasiconformal extensions. It had been a conjecture for a long time that the dilatations K0(h) and K1(h) are equal before Anderson and Hinkkanen disproved this by constructing concrete examples of a family of affine mappings of some parallelograms. The problem also engendered many interesting results. At the end of the current paper, we discuss relationships among K0(h), H(h) and K1(h) as a concluding remark.  相似文献   

4.
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   

5.
Previous research that compared the estimated parameters (i.e.,k andR e) from Herrnstein’s (1970) hyperbolic matching law equation within the same individuals responding for qualitatively different consummatory reinforcers (i.e., water and sucrose solution) found similar asymptotic response rates (k). The present study compared these parameters within subjects responding on levers for consummatory and nonconsummatory reinforcers. Male Wistar rats responded on a lever in a running wheel on a series of tandem FR 1 VI schedules for either 0.1 ml of a 15% sucrose solution or the opportunity to run for 15 sec. Herrnstein’s hyperbola was fit to response and reinforcement rates from each session. Results showed thatk values were significantly higher for sucrose than for wheel-running reinforcement. On average,R e was lower for sucrose than for wheel-running reinforcement, though not significantly lower. The results of the present study appear to violate the assumption of the constancy ofk in Herrnstein’s matching law analysis.  相似文献   

6.
In this article the development and validation of the Beliefs about Primary Education Scale (BPES) are described. The BPES is an 18-item scale for assessing primary school teachers’ beliefs toward the nature of good education, subdivided in a transmissive dimension (TD) and a developmental dimension (DD). Both dimensions assess beliefs toward the general orientation and objectives of education, the nature of the educational content, and desirable ways of knowledge acquisition. An explorative study (n=352n=352) revealed a two-factor structure. Both dimensions were uncorrelated, which leads to the suggestion that teachers hold layered belief systems. In a following study (n=381), construct validity of the BPES was confirmed. The BPES’ DD and TD were shown to correlate significantly with constructivist and traditional teaching beliefs.  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.
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   

9.
Let M‘ be a closed submanifold isometrically immersed in a unit sphere S^n p. Denote by R, H and S, the normalized scalar curvature, the mean curvature, and the square of the length of the second fundamental form of M‘, respectively. Suppose R is constant and ≥1. We study the pinching problem on S and prove a rigidity theorem for M‘ immersed in S^n p with parallel normalized mean curvature vector field. When n≥8 or, n=7 and p≤2, the pinching constant is best.  相似文献   

10.
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   

11.
Pascual‐Leone (1972) has conducted task analyses in terms of M‐demand (amount of information processing required by the task) and demonstrated that the phenomenon of ‘horizontal decalages’, described by Piaget, can be accounted for by increasing demands of information processing. It has been shown that formal operational reasoning is required to balance even simple, one‐step chemical equations, while formal reasoning and a sufficiently large M‐capacity are required to balance more complex, multi‐step chemical equations. The objective of the present study is to investigate the relation between functional M‐capacity (Mf) and student performance in solving chemistry problems of increasing M‐demand. It was found that student performance decreased as the M‐demand of the problems increased. Similarly, the correlation coefficients between Mf‐ and student performance increased progressively as the M‐demand of the problems increased.  相似文献   

12.
The study intends to examine the dimensions of teaching perceived by students in mathematics and their relations with attitudes towards mathematics (ATM) across genders. In this study, 602 students (Mage = 13.55, 48.34% male) from Chinese middle schools participated in a questionnaire assessing their perceptions of general and content-focused instruction and ATM. The Rasch model demonstrated that the six-factor model of classroom teaching is superior to one-factor and two-factor (i.e., general and content-focused instruction) models. The links between dimensions of teaching and attitude compositions were shown to be different across genders. Further, dimensions of teaching were important for boys' enjoyment and value and girls' boredom and self-concept in mathematics. Lastly, compared to content-focused instruction, the explanation degree of the general instruction to ATM is higher in both boys and girls.  相似文献   

13.
The dysregulation of social fear has been widely studied in children's shyness, but we know little about how shy children regulate during unfair treatment. We first characterized developmental patterns of children's shyness (N = 304, ngirls = 153; 74% White, 26% Other) across 2 (Mage = 2.07), 3 (Mage = 3.08), 4 (Mage = 4.08), and 6 (Mage = 6.58) years of age. Data collection occurred from 2007 to 2014. At age 6, the high stable group had higher cardiac vagal withdrawal and lower expressed sadness and approach-related regulatory strategy than the low stable group when being treated unfairly. Although shy children may be more physiologically impacted by being treated unfairly, they may mask their sadness to signal appeasement.  相似文献   

14.
Due to their significant value in both economy and ecology, Daphnia had long been employed to investigate in vivo response of cholinesterase (ChE) in anticholinesterase exposures, whereas the type constitution and property of the enzyme remained unclear. A type of ChE was purified from Daphnia magna using a three-step procedure, i.e., Triton X-100 extraction, ammonium sulfate precipitation, and diethylaminoethyl (DEAE)-Sepharose?-Fast-Flow chromatography. According to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), molecular mass of the purified ChE was estimated to be 84 kDa. Based on substrate studies, the purified enzyme preferred butyrylthiocholine iodide (BTCh) [with maximum velocity (V max)/Michaelis constant (K m)=8.428 L/(min·mg protein)] to acetylthiocholine iodide (ATCh) [with V max/K m=5.346 L/(min·mg protein)] as its substrate. Activity of the purified enzyme was suppressed by high concentrations of either ATCh or BTCh. Inhibitor studies showed that the purified enzyme was more sensitive towards inhibition by tetraisopropylpyrophosphoramide (iso-OMPA) than by 1,5-bis(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284C51). Result of the study suggested that the purified ChE was more like a type of pseudocholinesterase, and it also suggested that Daphnia magna contained multiple types of ChE in their bodies.  相似文献   

15.
ABSTRACT

The study aimed to investigate variations in addition and subtraction fluency by observing grade three students in Norway (n = 253, Mage = 8.38 y.) and Finland (n = 209, Mage = 9.35 y.) while controlling for their age and non-verbal reasoning. Gender differences were also examined. The focus of the study was on the performance of the low-achieving (LA) students in comparison to the typically achieving (TA) group, not neglecting differences in how early educational support was organised across the two countries. Two-minute speed tests in both addition and subtraction within the 1–20 number range were used to assess fluency. The Finnish students outperformed students in the Norwegian sample both in addition and subtraction fluency. There were more Norwegian students in the LA group (i.e. performance at or below the 25th percentile) in both addition (37.9% vs. 20.1%) and subtraction (39.1% vs. 15.8%). In comparison to the TA students, the LA students made more errors and skipped over more arithmetic tasks in an attempt to solve them. Observed differences are discussed in relation to both country characteristics concerning early mathematics education and early educational support.  相似文献   

16.
Enantiomers (R(+) and S(-)),RS-racemate (double compound) and (R+S)-conglomerate (mechanical mixture of enantiomers) of malic acid C 4 H 6 O 5 have been investigated by means of X-ray diffractometry and high temperature X-ray diffraction method.The RS-racemate was found to be able to form three polymorphic modifications,which we denominated as M1 (monoclinic,space group P2 1 /c),M2 (monoclinic,space group Cc),and Tc (triclinic,space group P-1),the latter modification having been unknown before.Modification Tc was also described,and its Xray diffraction characteristics,including interplanar spacings d,hkl indices,unit cell parameters,were defined.In addition,X-ray diffraction characteristics for both reported earlier M1 and M2 monoclinic polymorphic modifications were measured with higher accuracy.The ability of RS-racemate to form one of the above three modifications (M1,M2,and Tc) or their mixtures containing various proportions and combinations of the components (M1+M2,M1+Tc,or M2 +Tc) was found to depend on the type of crystallization medium (a melt,aqueous medium,ethanol or acetone solution),crystallization rate (from 2-3 minutes to 4 months),and crystallization temperature.Heating S-enantiomer and M1 RS-racemate up to their respective melting points (100 ℃ and 124 ℃,correspondingly) only made them undergo thermal deformations,while heating (R+S)-conglomerate in the temperature range of 96-110 ℃ resulted in its homogenization to form M2 RS-racemate,which,near the melting point (118 ℃),namely,in the range of 112-116 ℃,was transformed into M1 RS-racemate.  相似文献   

17.
Suppose {X, X n ;n≥1} is a sequence i.i.d.r.v. withEX=0 andEX 2<∞. Shao (1995) proved a conjecture of Révész (1990); ifP(X=±1)=1/2, then
. Furthermore he conjectured that
. In this paper we prove that if then this conjecture is ture. Project (10071072) supported by National Natural Science Foundation of China(NSFC).  相似文献   

18.
对有限个固定工件,n个自由工件的单机排序问题1｜FB（F）｜max wjCj进行了研究,证明该问题在F≥2的情况下不存在最坏性能比为2n的多项式时间近似算法;对只有一个固定工件,（maxwi1≤i≤n）/（minwi1≤i≤n）=c与输入无关的情形,设计了时间界为O（2c/εn＋nlogn）的多项式时间近似方案.  相似文献   

19.
For non-negative integers k, n, let P k (n) denote the sum {fx27-1}. We show by two different means that if k ≥ 3 and odd, then n 2(n+1)2 iss a factor of the polynomial P k (n); and if k ≥ 2 and even, then n (n+1) (2n+1) is a factor of the polynomial P k (n). We also derive a relatively unknown result first obtained by Johann Faulhaber in the 17th century. Shailesh Shirali has been at Rishi Valley School, Andhra Pradesh (Krishnamurti Foundation India) since the 1980’s. He has a deep interest in teaching and writing about mathematics at the high school/post school levels, with particular emphasis on problem solving and on historical aspects of the subject. He has been involved in the Mathematics Olympiad movement at the national and international level for the past two decades. He is the author of several expository books and articles aimed at interested high school students.  相似文献   

20.
The line persistence of a graph G, Pt （ G ） is the minimum number of lines which must be removed to increase the diameter of G. In Ref. [7] （J. Shanghai Univ., 2003,7（4）：352-357）, we gave a characterization of graphs of diameter five with ρ1 （ G ）≥2. In this paper we will show that each of the 8 special graphs Xi （ i = 1,2,3,4,5,6,7,8） listed in condition （2） of Theorem 1 in Ref. [7] can not be deleted. Therefore the results we obtained in Ref. [7] can not in general be improved.  相似文献   

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