Search results for "statistical"
showing 10 items of 4960 documents
Clinical value of increased serum creatinine concentration as predictor of short-term outcome in decompensated cirrhosis
2004
The purpose of this study was to assess whether serum creatinine concentration alone or associated with other biological parameters was an independent predictor of short-term mortality in patients with decompensated cirrhosis.A total of 212 consecutive episodes of decompensated cirrhosis in patients admitted to the hospital between January 1999 and December 2001 were reviewed retrospectively. Depending on a serum creatinine concentration equal to or greater than 1.5 mg/dL at the time of admission, patients were divided into decompensated cirrhosis with renal failure (101 episodes in 59 patients, aged 69.8 +/- 10 years) and without renal failure (111 episodes in 61 patients, aged 64.5 +/- 13…
Iterative approach to the exponential representation of the time–displacement operator
2005
An iterative method due to Voslamber is reconsidered. It provides successive approximations for the logarithm of the time–displacement operator in quantum mechanics. The procedure may be interpreted, a posteriori, as an infinite re-summation of terms in the so-called Magnus expansion. A recursive generator for higher terms is obtained. From two illustrative examples, a detailed comparative study is carried out between the results of the iterative method and those of the Magnus expansion.
Quantitative analysis of crystal/grain sizes and their distributions in 2D and 3D
2011
Abstract We review methods to estimate the average crystal (grain) size and the crystal (grain) size distribution in solid rocks. Average grain sizes often provide the base for stress estimates or rheological calculations requiring the quantification of grain sizes in a rock’s microstructure. The primary data for grain size data are either 1D (i.e. line intercept methods), 2D (area analysis) or 3D (e.g., computed tomography, serial sectioning). These data have been used for different data treatments over the years, whereas several studies assume a certain probability function (e.g., logarithm, square root) to calculate statistical parameters as the mean, median, mode or the skewness of a cr…
Guide to Practical Work with the Monte Carlo Method
2002
The guide is structured such that we proceed from the “easy” simulation methods and algorithms to the more sophisticated. For each method the algorithms are presented by the technique of stepwise refinement. We first present the idea and the basic outline. From then on we proceed by breaking up the larger logical and algorithmic structures into smaller ones, until we have reached the level of single basic statements. Sometimes we may elect not to go to such a depth and the reader is asked to fill in the gaps.
Immigrant status, gender, and school burnout in Finnish lower secondary school students : A longitudinal study
2017
The aim of this longitudinal study among 9223 students from grade 7 and grade 9 (age 13–14 and 15–16) was to assess whether immigrant status and gender are associated with the level and change (slope) in school burnout among lower secondary school students in the Helsinki metropolitan area. Ninety-seven percent of the variation in school burnout was attributable to individual factors. Both the intercept (2.3, p < 0.001) and slope (0.5, p < 0.001) of school burnout were statistically significant. The slope showed increasing school burnout from grades 7–9. School burnout increased more in girls than in boys. Initially apparent higher school burnout among students who had immigrated to …
Statistical Modeling of Huffman Tables Coding
2005
An innovative algorithm for automatic generation of Huffman coding tables for semantic classes of digital images is presented. Collecting statistics over a large dataset of corresponding images, we generated Huffman tables for three images classes: landscape, portrait and document. Comparisons between the new tables and the JPEG standard coding tables, using also different quality settings, have shown the effectiveness of the proposed strategy in terms of final bit size (e.g. compression ratio).
Optimized adiabatic passage with dephasing
2008
We study adiabatic population transfer with dephasing in two-level models driven by a chirped driving field. We show that the population transfer is maximized when the dynamics follows specific ellipses as trajectories in the parameter space. We determine the optimal parameters and estimate the losses in a closed form. These estimates show a similar robustness as for the standard lossless adiabatic processes with respect to variations of the parameters.
Mixed complexes of alkaline earth uranyl cabonates: A laser-induced time-resolved fluorescence spectroscopic study
2008
The interaction of the alkaline earth ions Mg2+, Sr2+ and Ba2+ with the uranyl tricarbonate complex has been studied by time resolved laser-induced fluorescence spectroscopy. In contrast to the non-luminescent uranyl tricarbonate complex the formed products show slight luminescence properties. These have been used to determine the stoichiometry and complex stabilities of the formed compounds. As the alkaline earth elements are located in an outer shell of the complex the influence of the type of the alkaline earth element on the stability constant is not very drastic. Therefore all obtained data were averaged in order to derive an common stability constant for the described complexes. These…
Invariant varieties of discontinuous vector fields
2004
We study the geometric qualitative behaviour of a class of discontinuous vector fields in four dimensions around typical singularities. We are mainly interested in giving the conditions under which there exist one-parameter families of periodic orbits (a result that can be seen as one analogous to the Lyapunov centre theorem). The focus is on certain discontinuous systems having some symmetric properties. We also present an algorithm which detects and computes periodic orbits.
Dynamics of the Shapovalov mid-size firm model
2020
Forecasting and analyses of the dynamics of financial and economic processes such as deviations of macroeconomic aggregates (GDP, unemployment, and inflation) from their long-term trends, asset markets volatility, etc., are challenging because of the complexity of these processes. Important related research questions include, first, how to determine the qualitative properties of the dynamics of these processes, namely, whether the process is stable, unstable, chaotic (deterministic), or stochastic; and second, how best to estimate its quantitative indicators including dimension, entropy, and correlation characteristics. These questions can be studied both empirically and theoretically. In t…