基于小波的带Hilbert核的奇异积分方程的解法

许多力学和工程问题都可以表示为第一类奇异积分方程.本文给出了带Hilbert核的奇异积分方程的小波Galerkin算法.利用L²([0,1])上的周期小波和Hilbert核的特点降低刚性矩阵的维数;并且通过阈值使得矩阵更加稀疏,以减少计算量和节省存储空间.根据Hilbert核的奇异性,通过Tikhonov正则化方法求解了所得到的刚性方程组,给出了算法的收敛性和数值结果.     

Analysis of abnormal intra-QRS potentials. Improved predictive value for arrhythmic events with the signal-averaged electrocardiogram

BACKGROUND: Using the signal-averaged ECG (SAECG), this study developed a new electrical index for predicting arrhythmic events: abnormal intra-QRS potentials (AIQP). METHODS AND RESULTS: We studied 173 patients followed after myocardial infarction for a mean duration of 14 +/- 7 months. Sixteen arrhythmic events occurred, defined as sudden cardiac death, documented sustained ventricular tachycardia, or non-fatal cardiac arrest. Noninvasive indices of arrhythmia risk were measured, including AIQP, conventional SAECG, Holter, and left ventricular ejection fraction (LVEF). Abnormal intra-QRS potentials were defined as abnormal signals occurring anywhere within the QRS period. They were estimated with a lead-specific, parametric modeling method that removed the smooth, predictable part of the QRS. AIQPs are characterized by the remaining transient, unpredictable component of the QRS and manifest as low-amplitude notches and slurs. A combined XYZ-lead AIQP index exhibited higher specificity (95%) and predictive value (PV) (+PV, 47%; -PV, 94%) than the conventional SAECG in combination with Holter and LVEF (specificity, 89%; +PV, 25%; -PV, 93%). CONCLUSIONS: AIQP improved specificity and predictive value, compared with conventional tests, for prediction of arrhythmic events. AIQP emerged as the best noninvasive univariate predictor of arrhythmic events after myocardial infarction in this study. A review of several other reports shows that AIQP in the present study outperformed the conventional predictive indices reported in those other data sets.     

Structural equation modeling with longitudinal data: Strategies for examining group differences and reciprocal relationships.

This article describes the use of structural equation modeling with latent variables to examine group differences and test competing models about cause–effect relationships in passive longitudinal designs. This approach is compared with several other statistical methods including analysis of cross-lagged panel correlations, regression analysis, and path analysis. The mechanics and advantages of structural equation modeling are illustrated using an example based on a 3-wave longitudinal study of adolescents' alcohol use. Within this example, the generalizability of the measurement model and structural model are assessed across gender and time, and competing models about the causes and consequences of adolescents' alcohol use are tested. The article concludes with a discussion of some of the strengths and limitations of using structural equation modeling with longitudinal data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of nonnormality on full information maximum-likelihood estimation for structural equation models with missing data.

A Monte Carlo simulation examined full information maximum-likelihood estimation (FIML) in structural equation models with nonnormal indicator variables. The impacts of 4 independent variables were examined (missing data algorithm, missing data rate, sample size, and distribution shape) on 4 outcome measures (parameter estimate bias, parameter estimate efficiency, standard error coverage, and model rejection rates). Across missing completely at random and missing at random patterns, FIML parameter estimates involved less bias and were generally more efficient than those of ad hoc missing data techniques. However, similar to complete-data maximum-likelihood estimation in structural equation modeling, standard errors were negatively biased and model rejection rates were inflated. Simulation results suggest that recently developed correctives for missing data (e.g., rescaled statistics and the bootstrap) can mitigate problems that stem from nonnormal data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Compared with what? The effects of different comparisons on conceptual knowledge and procedural flexibility for equation solving.

Researchers in both cognitive science and mathematics education emphasize the importance of comparison for learning and transfer. However, surprisingly little is known about the advantages and disadvantages of what types of things are being compared. In this experimental study, 162 seventh- and eighth-grade students learned to solve equations (a) by comparing equivalent problems solved with the same solution method, (b) by comparing different problem types solved with the same solution method, or (c) by comparing different solution methods to the same problem. Students’ conceptual knowledge and procedural flexibility were best supported by comparing solution methods and to a lesser extent by comparing problem types. The benefits of comparison are augmented when examples differ on relevant features, and contrasting methods may be particularly useful in mathematics learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aversive schedules with independent probabilities of reinforcement for responding and not responding by rhesus monkeys: III. Recovery of avoidance baseline.

Investigated the effect of prior response history on subsequent avoidance responding. In Exps I and II, using 12 and 10 male rhesus monkeys that had served in previous experiments by the authors (see PA, Vol 53:Issue 6), up to 5 sequences of aversive stimulus presentation schedules provided a range from no responding to complete avoidance response recovery, whether with or without signaled shock. Exp III, with 12 naive rhesus monkeys, demonstrated that the same range of avoidance response recovery could be obtained by the use of only selected schedules rather than a prolonged sequence. These findings provide further support for the power of 2 independent probability variables, governing reinforcement delivery for responding or nonresponding, for generating schedules of reinforcement. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reactor models for a series of continuous stirred tank reactors with a gas-liquid-solid leaching system: Part III. Model application

A mathematical model developed to describe the steady-state performance of a three-phase leaching reactor is applied to the analysis and simulation of an industrial process: the high-temperature (180 °C to 200 °C) aqueous pressure oxidation (O₂-H₂SO₄) of refractory pyrite-arsenopyrite (FeS₂-FeAsS) gold concentrates. The simulation work reported here centers on the analysis of the autothermal operation of a continuous multistage horizontal autoclave. The focus is on the performance of the first autoclave compartment, since its autothermal “initialization” determines the rate of the whole process. The analysis of the whole autoclave is subsequently done on a stage-by-stage basis. The model considers both possible reaction control regimes, that is, reactor operation limited by the rate of the particle dissolution reaction (surface reaction control)or limited by the rate of O₂ transfer at the g-1 interface (gas-transfer control). The decision whether the reactor operates under surface reaction control or gas transfer control is based on whether the gas-transfer capacity of the reactor can or cannot satisfy the oxygen demands of the leaching reactions. With the aid of the model, the effects of feed rate, feed preheating, cooling with water injection, slurry recycling, and autoclave configuration are critically evaluated from the standpoint of optimum autoclave performance.     

Growth curve models for indistinguishable dyads using multilevel modeling and structural equation modeling: The case of adolescent twins' conflict with their mothers.

Growth modeling is a useful tool for studying change over time, and it is becoming increasingly popular with developmental researchers. There is a considerable methodological literature surrounding growth modeling for individuals; however, far less attention has been focused on growth models for pairs of related individuals (i.e., dyads). In this article, the authors consider dyadic growth models for those cases where there are no relevant variables that can empirically distinguish between dyad members (e.g., same-sex twins or best friends). The authors describe how researchers can estimate growth models for indistinguishable dyads using both multilevel modeling and structural equation modeling. Although both approaches can be used to estimate the same underlying models, the authors focus on practical similarities and differences between the two approaches. They illustrate modeling issues using an overtime study of adolescent twins' conflict with their mothers, a substantively important topic given the enduring interest in parent-child relationships during adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A partially functional DNA helicase II mutant defective in forming stable binary complexes with ATP and DNA. A role for helicase motif III

To address the functional significance of motif III in Escherichia coli DNA helicase II, the conserved aspartic acid at position 248 was changed to asparagine. UvrDD248N failed to form stable binary complexes with either DNA or ATP. However, UvrDD248N was capable of forming an active ternary complex when both ATP and single-stranded DNA were present. The DNA-stimulated ATPase activity of UvrDD248N was reduced relative to that of wild-type UvrD with no significant change in the apparent Km for ATP. The mutant protein also demonstrated a reduced DNA unwinding activity. The requirement for high concentrations of UvrDD248N to achieve unwinding of long duplex substrates likely reflects the reduced stability of various binary and ternary complexes that must exist in the catalytic cycle of a helicase. The data suggest that motif III may act as an interface between the ATP binding and DNA binding domains of a helicase. The uvrDD248N allele was also characterized in genetic assays. The D248N protein complemented the UV-sensitive phenotype of a uvrD deletion strain to levels nearly equivalent to wild-type helicase II. In contrast, the mutant protein only partially complemented the mutator phenotype. A correlation between the level of genetic complementation and the helicase activity of UvrDD248N is discussed.