Bayesian Joint Modeling of Skew-Positive Longitudinal-Survival Data Using Birnbaum-Saunders Distribution

Background: There has been a great interest in joint modeling of longitudinal and survival data in recent two decades. Joint models have less restrictive assumptions in multivariate modeling and could address various research questions. This has led to their wide applications in practice. However, earlier models had normality assumption on the distribution in longitudinal part that is usually violated in real data. Hence, recent research have focused on circumventing this issue. Using various skewed distributions has been proposed and applied in the literature. Nevertheless, the flexibility of the proposed methods is limited especially when the data are skew positive. Methods: In this paper, we introduce the use of Birnbaum-Saunders (BS) distribution in joint modeling context. BS distribution is more flexible and could cover a wide range of skew, kurtotic or bimodal data. Results: We analyzed publicly available ddI/ddC data both with normal and BS distributions in Bayesian setting and compared their fit by Widely Applicable Information Criterion (WAIC). The joint BS model showed a better fit to the data. Conclusion: We introduced and applied BS distribution in joint modeling of longitudinal-survival data. Using multi-parameter distributions such as BS in Bayesian setting could improve the fit of models without limitations that arise in transformation of data from original scale.

P751 Prevalence and risk factors of non-alcoholic fatty liver disease in inflammatory bowel diseases

Background Non-alcohol fatty liver disease (NAFLD) is a widespread disease in Europe with a prevalence of 20–30% in the German population. Some studies have revealed even higher prevalence in patients with inflammatory bowel diseases (IBD). The majority of prior studies on this subject are cross-sectional analyses. Longitudinal data for the identification of prognostic parameters are missing. Methods This is a monocentric retrospective study encompassing both a cross-sectional and a longitudinal part. The study included 440 patients with Crohn’s disease (CD) and 254 patients with ulcerative colitis (UC). Inclusion criteria were diagnosis of IBD, age >17 years, and having received at least one abdominal ultrasound of the liver at the IBD outpatient clinic of the Heidelberg University Hospital. Exclusion criteria were presence of any infectious liver disease, alcoholic fatty liver disease, or documented abuse of alcohol. NAFLD was defined by echogenicity via ultrasoud and assigned in degrees of severity (no, mild, moderate or severe steatosis). As potential risk factors for the development of NAFLD, demographic characteristics, IBD activity (clinical scores, laboratory results, endoscopic or ultrasound findings), and IBD medications were investigated. Results The prevalence of NAFLD was 48% in CD patients and 44% in UC patients. Higher age and body mass index (BMI) were significantly associated with the occurrence of NAFLD. NAFLD was associated with higher Harvey Bradshaw Index in CD patients, while laboratory results, endoscopic or ultrasound findings proving inflammation were not associated with NAFLD. In UC patients, there was no association between disease activity and NAFLD. The use of steroids, immunomodulators or biologics was not associated with NAFLD, while the use of sulfasalazine was associated with NAFLD only in CD patients. In the longitudinal part of this study, 2467 hepatic ultrasound results were included. Age and BMI in CD patients and BMI in UC patients were significant risk factors in the mixed logistic regression model. Also, in CD patients, higher HBI, former bowel resections, endoscopic disease activity and use of azathioprine–not of steroids–were risk factors of NAFLD. In UC patients, endoscopic disease activity was significantly associated with NAFLD in the mixed logistic regression model. Conclusion There is a high prevalence of NAFLD in German IBD patients. The risk to develop NAFLD increases in older patients and patients with higher BMI. Disease activity and azathioprine use in CD may increase the prevalence of NAFLD. Our study provides a rationale for regular ultrasound screening of the liver in IBD patients.

Structural-Tectonic and Geomorphological Features of the Longitudinal Part of the Koyva River

The features of the geomorphological structure of the Koyva River valley in the Gornozavodskiy district of Perm Krai are considered. The leading role of tectonics in formation of terraces and development of the valley of the longitudinal (relative to the folded structures of the Urals) area of the upper and middle courses is shown. The development of regional faults and thrusts at the base of the valley is associated with the formation of the Vishersko-Visimskaya depression. The formation of gold - and platinum-bearing placers is associated with the terraces location and the orientation of the Koyva River Valley.

Continuity with the Past and Uncertainty for the Future

The article examines the newspaper constructions of religion in Danishnewspapers in a quantitative longitudinal analysis from 1750 to 2000and a more qualitative analysis of recent news production from thelast forty years. For the longitudinal part, the database of the digitization of Danish newspapers project is used. Using the available toolsfor quantitative data analysis, the article shows that the category ofreligion and world religions has been visible in Danish newspaperssince 1750. The coverage of world religions is often related to thecoverage of international news. Overall, the article documents a remarkable continuity of the presence of religion. Examining the morerecent material qualitatively, the article shows that although manyreligions have been historically visible in the news, they have mostrecently become more frequent in the debate sections than in thenews sections. It is primarily Islam that is debated. This is connectedwith a shift from religious diversity as part of foreign news coverageto domestic news coverage, related to changes in the surroundingDanish society. Nevertheless, the coverage of Islam also displays aremarkable continuity.

A Longitudinal Study of Growth, Sex Steroids, and IGF-1 in Boys With Physiological Gynecomastia

Context: Physiological gynecomastia is common and affects a large proportion of otherwise healthy adolescent boys. It is thought to be caused by an imbalance between estrogen and testosterone, although this is rarely evident in analyses of serum. Objective: This study aimed to describe the frequency of physiological gynecomastia and to determine possible etiological factors (eg, auxology and serum hormone levels) in a longitudinal setup. Design, Settings, and Participants: A prospective cohort study of 106 healthy Danish boys (5.8–16.4 years) participated in the longitudinal part of the COPENHAGEN Puberty Study. The boys were examined every 6 months during an 8-year follow-up. Median number of examinations was 10 (2–15). Main outcome measurements: Blood samples were analyzed for FSH, LH, testosterone, estradiol, SHBG, inhibin B, anti-Müllerian hormone, IGF-1, and IGF binding protein-3 by immunoassays. Auxological parameters, pubertal development, and the presence of gynecomastia were evaluated at each visit. Results: Fifty-two of 106 boys (49%) developed gynecomastia, of which 10 (19%) presented with intermittent gynecomastia. Boys with physiological gynecomastia reached peak height velocity at a significantly younger age than boys who did not develop gynecomastia (13.5 versus 13.9 years, P = .027), and they had significantly higher serum levels of IGF-1 (P = .000), estradiol (P = .013), free testosterone (P < .001), and FSH (P = .030) during pubertal transition. However, no differences in serum LH or in the estradiol to testosterone ratio were found. Conclusions: Gynecomastia is frequent in pubertal boys. Increased IGF-1 levels and pubertal growth appear to be associated, whereas changes in estrogen to testosterone ratio seem negligible.

Longitudinal–transverse aerodynamic force in viscous compressible complex flow

We report our systematic development of a general and exact theory for diagnosis of total force and moment exerted on a generic body moving and deforming in a calorically perfect gas. The total force and moment consist of a longitudinal part (L-force) due to compressibility and irreversible thermodynamics, and a transverse part (T-force) due to shearing. The latter exists in incompressible flow but is now modulated by the former. The theory represents a full extension of a unified incompressible diagnosis theory of the same type developed by J. Z. Wu and coworkers to compressible flow, with Mach number ranging from low-subsonic to moderate-supersonic flows. Combined with computational fluid dynamics (CFD) simulation, the theory permits quantitative identification of various complex flow structures and processes responsible for the forces, and thereby enables rational optimal configuration design and flow control. The theory is confirmed by a numerical simulation of circular-cylinder flow in the range of free-stream Mach number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}M_{\infty }$ between 0.2 and 2.0. The L-drag and T-drag of the cylinder vary with $M_{\infty }$ in different ways, the underlying physical mechanisms of which are analysed. Moreover, each L-force and T-force integrand contains a universal factor of local Mach number $M$. Our preliminary tests suggest that the possibility of finding new similarity rules for each force constituent could be quite promising.

Habitual Self–Control: A Brief Measure of Persistent Goal Pursuit

Habitual self–control is defined as a trait–like personal resource factor that facilitates the enactment of difficult intentions. A 14–item Habitual Self–Control Questionnaire (HSCQ) was developed to assess this trait. Reliability, factorial validity, and criterion validity were assessed in five undergraduate student subsamples with an overall N of 2224. Internal consistency was .81 across the entire sample, and test–retest reliability was .83 over a one–month interval. The HSCQ showed a theoretically meaningful pattern in terms of convergent and discriminant validity and criterion validity in predicting a variety of health behaviours that relate to self–control, including exercise, dieting behaviour, binge eating and weight loss success. Further, the HSCQ contributed uniquely to the prediction of health behaviours beyond alternative self–control scales. In a longitudinal part of the study, the HSCQ added to the prediction of action plan completion and satisfaction beyond motivation and moderated the relationship between motivation and enactment of action plans as theoretically expected. In sum, the results provided strong evidence for the reliability and validity of the HSCQ and highlighted some theoretically meaningful differences to already existing measures of self–control. Theoretical implications are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

A Semi-Analytical Finite Strip for the Analysis of Folded Plates

In the conventional semi-analytical finite strip analysis of folded plates, the boundary conditions and the intermediate support conditions must be satisfieda priori. The admissible functions used as the longitudinal part of the displacement functions are sometimes difficult to find, and they are valid for specific conditions only. In this paper, a general semi-analytical finite strip is developed for the analysis of folded plate structures. The geometric constraints of the folded plates, such as the conditions at the end and intermediate supports, are modelled by very stiff translational and rotational springs, as appropriate. The complete Fourier series including the constant term are chosen as the longitudinal approximating functions for each of the displacements. As these displacement functions are more general in nature and independent of one another, they are capable of giving more accurate solutions. The potential problem of ill-conditioned matrices is investigated and the appropriate choice of the very stiff springs is also suggested. The formulation is done in such a way to obtain a unified approach, taking full advantage of the power of modern computers. Numerical examples are presented for comparison with numerical results from published solutions or solutions obtained from the finite element method. The results show that this kind of strips is versatile, efficient and accurate for the analysis of folded plates.

PHONON EXCESS HEATING IN ELECTRONIC RELAXATION THEORY IN QUANTUM DOTS

When the usual operator of the Fröhlich's coupling between electrons and longitudinal optical phonons of semiconductor single quantum dot is used to calculate electronic energy relaxation, a permanent phonon generation in quantum dot is obtained, leading to an artificial effect of permanent heating up of the lattice. The mechanism of the phonon heating is identified here with the influence of the transverse part of the interaction operator. This part is responsible first of all for a tendency to build the polaronic well of an electron in a quantum dot. The effect of overheating is shown to be possibly eliminated to a considerable extent upon removing the transverse part of the interaction with the help of the Lang–Firsov canonical transformation and upon modifying accordingly the longitudinal part of the coupling. The resulting electronic relaxation and optical phonon generation is demonstrated numerically in a relatively simple approximation to electron and phonon self-energy, in which the model of quantum dot is reduced to an electron coupled to a single-LO-phonon mode. It is interesting to see that the removal of the phonon overheating based on the application of the Lang–Firsov canonical transformation has a rather small influence on electronic characteristics calculated with electronic transport equations. In this sense, the long-time limit properties of the electronic subsystem, like the electronic up-conversion and incomplete depopulation effect, calculated earlier, remain nearly untouched.

Propagation of electromagnetically generated wake fields in inhomogeneous magnetized plasmas

Generation of wake fields by a short electromagnetic pulse in a plasma with an inhomogeneous background magnetic field and density profile is considered, and a wave equation is derived. Transmission and reflection coefficients are calculated in a medium with sharp discontinuities. Particular attention is focused on examples where the longitudinal part of the electromagnetic field is amplified for the transmitted wave. Furthermore, it is noted that the wake field can propagate out of the plasma and thereby provide information about the electron density profile. A method for reconstructing the background density profile from a measured wake field spectrum is proposed and a numerical example is given.