Search results for " function"
showing 10 items of 9395 documents
First-order linear differential equations whose data are complex random variables: Probabilistic solution and stability analysis via densities
2022
[EN] Random initial value problems to non-homogeneous first-order linear differential equations with complex coefficients are probabilistically solved by computing the first probability density of the solution. For the sake of generality, coefficients and initial condition are assumed to be absolutely continuous complex random variables with an arbitrary joint probability density function. The probability of stability, as well as the density of the equilibrium point, are explicitly determined. The Random Variable Transformation technique is extensively utilized to conduct the overall analysis. Several examples are included to illustrate all the theoretical findings.
Binding of Escherichia coli hemolysin and activation of the target cells is not receptor-dependent.
2005
Abstract Production of a single cysteine substitution mutant, S177C, allowed Escherichia coli hemolysin (HlyA) to be radioactively labeled with tritiated N-ethylmaleimide without affecting biological activity. It thus became possible to study the binding characteristics of HlyA as well as of toxin mutants in which one or both acylation sites were deleted. All toxins bound to erythrocytes and granulocytes in a nonsaturable manner. Only wild-type toxin and the lytic monoacylated mutant stimulated production of superoxide anions in granulocytes. An oxidative burst coincided with elevation of intracellular Ca2+, which was likely because of passive influx of Ca2+ through the toxin pores. Competi…
The perception of the family functionality: Confirmation of its bifactorial structure
2012
Es necesario crear instrumentos válidos, fiables y de fácil aplicación para evaluar la funcionalidad familiar. En el presente estudio se confirma la estructura bifactorial de una Escala de Funcionalidad familiar de 23 ítems aportando índices de fiabilidad y validez externa en una muestra de 185 familias con hijos adolescentes. Se analiza la discrepancia parental, y se presentan los estadísticos descriptivos de esta variable en las dimensiones que constituyen la escala: Facilitador y Perturbador. El instrumento es útil para valorar la funcionalidad y para calcular la discrepancia parental en la percepción de la vida familiar, que es también un indicador de funcionalidad. Valid, reliable and …
Innovative Analysis of Service-Learning Effects in Physical Education: A Mixed-Methods Approach
2020
Purpose: To compare the development of teaching competency in preservice teachers of physical education (n = 96) through two different modalities of intervention from the same service-learning program. The preservice teachers provided a direct service to children with motor functional diversity, promoting their motor skills and counteracting their lack of social attention. Method: The topic was approached using mixed methods with methodological triangulation. Quantitative evidence was gathered through a quasi-experimental design of two nonequivalent experimental groups implementing the following instrument: the Teaching Competency while performing Motor Skills and Body Language Games Rubric…
Singularity tracking for Camassa-Holm and Prandtl's equations
2006
In this paper we consider the phenomenon of singularity formation for the Camassa-Holm equation and for Prandtl's equations. We solve these equations using spectral methods. Then we track the singularity in the complex plane estimating the rate of decay of the Fourier spectrum. This method allows us to follow the process of the singularity formation as the singularity approaches the real axis.
PIECEWISE SMOOTH REVERSIBLE DYNAMICAL SYSTEMS AT A TWO-FOLD SINGULARITY
2012
This paper focuses on the existence of closed orbits around a two-fold singularity of 3D discontinuous systems of the Filippov type in the presence of symmetries.
Properties and Structural Studies of Multi-Wall Carbon Nanotubes-Phosphate Ester Hybrids
2013
Long chain phosphate esters bearing at least one or two aryl groups have been synthesized and used for the preparation of stable multi-walled carbon nanotube (MWCNT) hybrids. The non-covalent interaction ester/MWCNT has been investigated by several techniques (SEM, UV-vis, 31P-NMR, RAMAN). The used phosphate ester derivatives demonstrated the ability to produce an excellent dispersion of MWCNT in CHCl3. The obtained dispersions showed a great stability from one to at least three weeks in the range of concentration considered. Thermal analysis showed an increase in the decomposition temperature for the hybrids with respect to pristine MWCNT.
When do Improved Covariance Matrix Estimators Enhance Portfolio Optimization? An Empirical Comparative Study of Nine Estimators
2010
The use of improved covariance matrix estimators as an alternative to the sample estimator is considered an important approach for enhancing portfolio optimization. Here we empirically compare the performance of 9 improved covariance estimation procedures by using daily returns of 90 highly capitalized US stocks for the period 1997-2007. We find that the usefulness of covariance matrix estimators strongly depends on the ratio between estimation period T and number of stocks N, on the presence or absence of short selling, and on the performance metric considered. When short selling is allowed, several estimation methods achieve a realized risk that is significantly smaller than the one obtai…
Labor productivity and firm-level TFP with technology-specific production functions
2020
Abstract We investigate the technological dimension of productivity, presenting an empirical methodology based on mixture models to disentangle the labor productivity differences associated with the firm's choice of technology (BTFP) and those related to the firm's ability to exploit the adopted technology (WTFP). The estimation endogenously determines the number of technologies (in the sector) and degree of technology sharing across firms (i.e., for each firm, the probability of using a given technology). By using comparable data for about 35,000 firms worldwide distributed across 22 (two-digit) sectors, we show BTFP to be at least as important as WTFP in explaining the labor productivity …
Estimation of Uncertain Relations between Indeterminate Temporal Points
2000
Many database applications need to manage temporal information and sometimes to estimate relations between indeterminate temporal points. Indeterminacy means that we do not know exactly when a particular event happened. In this case, temporal points can be defined within some temporal intervals. Measurements of these intervals are not necessarily based on exactly synchronized clocks, and, therefore, possible measurement errors need to be taken into account when estimating the temporal relation between two indeterminate points. This paper presents an approach to calculate the probabilities of the basic relations (before, at the same time, and after) between any two indeterminate temporal poi…