Impact of non-normal random effects on inference by multiple imputation: A simulation assessment

Multivariate extensions of well-known linear mixed-effects models have been increasingly utilized in inference by multiple imputation in the analysis of multilevel incomplete data. The normality assumption for the underlying error terms and random effects plays a crucial role in simulating the posterior predictive distribution from which the multiple imputations are drawn. The plausibility of this normality assumption on the subject-specific random effects is assessed. Specifically, the performance of multiple imputation created under a multivariate linear mixed-effects model is investigated on a diverse set of incomplete data sets simulated under varying distributional characteristics. Under moderate amounts of missing data, the simulation study confirms that the underlying model leads to a well-calibrated procedure with negligible biases and actual coverage rates close to nominal rates in estimates of the regression coefficients. Estimation quality of the random-effect variance and association measures, however, are negatively affected from both the misspecification of the random-effect distribution and number of incompletely-observed variables. Some of the adverse impacts include lower coverage rates and increased biases.     

Parent psychopathology, parenting, and child internalizing problems in substance-abusing families.

A structural model accounting for child internalizing problems in substance-abusing families was tested. Parents receiving substance abuse treatment (N = 242) completed forms about children between the ages of 6 and 18 who resided in their home. The effects of parent gender, child gender, and child age were controlled. Negative parenting was examined as a mediator between parent internalizing and externalizing problems and child anxiety and affective problems using path analysis. Negative parenting mediated relations only between parent internalizing problems and child affective problems. High-positive involvement moderated relations between parent externalizing problems and child internalizing problems. Relations between parent externalizing problems and child anxiety and affective problems were significant only among families in which high-positive involvement was present. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A class of adaptive directional image smoothing filters

The gray level distribution around a pixel of an image usually tends to be more coherent in some directions compared to other directions. The idea of adaptive directional filtering is to estimate the direction of higher coherence around each pixel location and then to employ a window which approximates a line segment in that direction. Hence, the details of the image may be preserved while maintaining a satisfactory level of noise suppression performance. In this paper we describe a class of adaptive directional image smoothing filters based on generalized Gaussian distributions. We propose a measure of spread for the pixel values based on the maximum likelihood estimate of a scale parameter involved in the generalized Gaussian distribution. Several experimental results indicate a significant improvement compared to some standard filters.     

Experimentelle und theoretische Untersuchungen über den Einfluß des Turbulenzgrads auf den Wärmeübergang in der Umgebung des Staupunkts eines Kreiszylinders

Zusammenfassung Es wurde der Einflu? des Turbulenzgrads T_u der Anstr?mung auf den W?rmeübergang in der Umgebung des Staupunkts eines Kreiszylinders theoretisch und experimentell untersucht. Dabei ?nderte man im Versuch den Turbulenzgrad der Anstr?mung durch Verwenden verschiedener Gitter von T_u=0,8 bis 5,2%. Die Messungen fanden bei kleinen Machzahlen (Ma<0,1) und bei Reynoldszahlen vonRe _D=0,8·10⁵ bis 1,12·10⁵ statt. Um den Mechanismus des W?rmeübergangs in Abh?ngigkeit vom Turbulenzgrad theoretisch zu kl?ren, untersuchte man die laminare Str?mungs- und die Temperaturgrenzschicht an einem Kreiszylinder für den Fall einer gest?rten Au?enstr?mung. Dabei legte man für die Staupunktstr?mung ein Modell mit St?rwirbeln alternierenden Drehsinns ?hnlich den Taylor-G?rtler-Wirbeln zugrunde, die in der Grenzschichtstr?mung einer Flüssigkeit l?ngs einer konkaven Wand entstehen. Die Integration der Grenzschichtgleichungen führt zu der Erkenntnis, da? ?nderungen der Wandschubspannung und des W?rmeübergangs nur von sekund?ren Effekten verursacht werden k?nnen und somit vom Turbulenzgrad der Str?mung sowie von der Wellenl?nge der St?rungen abh?ngen. In übereinstimmung mit den experimentellen Ergebnissen zeigen die theoretischen Rechnungen eine betr?chtliche Zunahme der W?rmeübergangs- und der Wandschubspannungswerte mit wachsendem Turbulenzgrad der Str?mung. Gekürzte Fassung der von der Fakult?t für Maschinenbau und Elektrotechnik der Technischen Universit?t Braunschweig im Jahr 1968 genehmigten gleichnamigen Dissertation des Verfassers. Die ausführliche Fassung liegt als Bericht des Instituts für Str?mungsmechanik der Technischen Universit?t Braunschweig von [12]. Die Dissertation entstand w?hrend eines vierj?hrigen Studienaufenthaltes (1964 bis 1968) des Verfassers unter Betreuung durch Prof. Dr.-Ing.K. Gersten am genannten Institut (Leiter Prof. Dr.-Ing. E. h. Dr. phil.H. Schlichting).     

Solvent swelling studies of Göynük (Kerogen Type-I) and Beypazar? oil shales (Kerogen Type-II)

The volumetric swelling procedure was applied to Göynük and Beypazar? oil shales from Turkey by using 10 solvents and the cross-linking in the macromolecular network of oil shales were investigated using this technique. Results from solvent swelling measurements show that the volumetric solvent swelling of oil shales samples roughly follows the regular solution theory. The theory of solvent swelling of cross-linked polymers developed Flory-Rehner and extension of this theory by Kovac-Peppas was used to calculate number average molecular weight per cross-link of kerogen structure in oil shale samples. Results indicate no remarkable difference between values for Göynük oil shale (Kerogen Type I) and Beypazar? oil shale (Kerogen Type II).     

Capacitive micromachined ultrasonic transducers with diffraction-based integrated optical displacement detection

Capacitive detection limits the performance of capacitive micromachined ultrasonic transducers (CMUTs) by providing poor sensitivity below megahertz frequencies and limiting acoustic power output by imposing constraints on the membrane-substrate gap height. In this paper, an integrated optical interferometric detection method for CMUTs, which provides high displacement sensitivity independent of operation frequency and device capacitance, is reported. The method also enables optoelectronics integration in a small volume and provides optoelectronic isolation between transmit and receive electronics. Implementation of the method involves fabricating CMUTs on transparent substrates and shaping the electrode under each individual CMUT membrane in the form of an optical diffraction grating. Each CMUT membrane thus forms a phase-sensitive optical diffraction grating structure that is used to measure membrane displacements down to 2/spl times/10/sup -4/ /spl Aring///spl radic/Hz level in the dc to 2-MHz range. Test devices are fabricated on quartz substrates, and ultrasonic array imaging in air is performed using a single 4-mm square CMUT consisting of 19/spl times/19 array of membranes operating at 750 kHz.     

Determination of neotectonic features of the Karasu Basin (SE Turkey) and their relationship with Quaternary volcanic activity using Landsat ETM+ imagery

The junction between the East Anatolian and the Dead Sea fault zones lies close to an unstable F: Transform fault (FFF) triple junction where the African, Eurasian and Arabian plates meet in south-eastern Turkey. The Karasu Basin is an ephemeral rifted structure located close to the junction of these plate boundaries and is expressed by a range of tectono-morphological features. This study uses remote sensing to define tectonic structures and discriminate volcanic rocks linked to rifting within the basin using Landsat Enhanced Thematic Mapper Plus (ETM+) imagery. Prior to advanced image processing stages, images were corrected to eliminate atmospheric scattering effects and determine the best band combination for multi-spectral processing techniques based on statistical methods. Following pre-processing stages, edge detection filters were applied to derive tectonic structures defining the basin. The Brovey transformation, a statistical data merging method, was used to combine reflective multi-spectral bands with the Landsat ETM+?panchromatic band. This method fuses higher spatial data with data of lower spatial value. The western margin of the Karasu Basin is defined by the left-lateral Amanos Fault Zone with a contemporary motion (c. –0.4 mm a^?1) probably accommodating most of the left-lateral strike-slip motion between Arabian and African plates on the northern continuation of the Dead Sea Fault Zone. The rift zone has been the site of extensive recent volcanism concentrated within the Brunhes Chron (<0.78 Ma) and linked to fault block rotations between the intracontinental master faults. The boundaries of this activity are defined here using a regolith mapping technique.     

3D Model compression using Connectivity-Guided Adaptive Wavelet Transform built into 2D SPIHT

Connectivity-Guided Adaptive Wavelet Transform based mesh compression framework is proposed. The transformation uses the connectivity information of the 3D model to exploit the inter-pixel correlations. Orthographic projection is used for converting the 3D mesh into a 2D image-like representation. The proposed conversion method does not change the connectivity among the vertices of the 3D model. There is a correlation between the pixels of the composed image due to the connectivity of the 3D mesh. The proposed wavelet transform uses an adaptive predictor that exploits the connectivity information of the 3D model. Known image compression tools cannot take advantage of the correlations between the samples. The wavelet transformed data is then encoded using a zero-tree wavelet based method. Since the encoder creates a hierarchical bitstream, the proposed technique is a progressive mesh compression technique. Experimental results show that the proposed method has a better rate distortion performance than MPEG-3DGC/MPEG-4 mesh coder.     

Optimization of microwave baking of model layer cakes

 Response surface methodology was used to optimize the formulation of microwave-baked cakes. The independent variables were water content, emulsifier content baking time, oven power, shortening content and starch type. The quality factors evaluated were specific gravity of batter and volume index, uniformity index and tenderness of the crumb. Constraints for quality factors were obtained by conventional baking of American Association of Cereal Chemists high-ratio cake formulation. Multiple contour plots showed the optimum region for various water and shortening combinations at different emulsifier, time and power levels. Cakes formulated with wheat starch, containing 0.3% polysorbate 60, 133.7% water and 45.2% shortening (flour substitute basis), baked for 6 min at 100% power yielded acceptable cakes that can compete with conventionally baked cakes. Rice and corn cakes had lower quality than conventionally baked high-ratio cakes. Power was found to be the most efficient independent variable affecting all the dependent variables. Received: 26 August 1999 / Revised version: 11 October 1999