Search results for "equation"
showing 10 items of 4219 documents
Spanish Adaptation of the Inventory Brief Child Abuse Potential and the Protective Factors Survey
2021
Child maltreatment is a public health problem with different consequences depending on the form of abuse. Measuring risk and protective factors has been a fertile ground for research, without involving instruments with sufficient evidence of validity. The aim of the study was to gather evidence of validity and reliability of the Inventory Brief Child Abuse Potential (IBCAP) and Protective Factors Survey (PFS) in the Mexican population. The instruments were translated into Spanish. In a non-probabilistic sample of 200 participants, the 7-factor model for the IBCAP [comparative fit index (CFI) = 0.984; root mean square error of approximation (RMSEA) = 0.067] and the 4-factor model for the PFS…
Classical and quantum aspects of electric-magnetic duality rotations in curved spacetimes
2018
It is well known that the source-free Maxwell equations are invariant under electric-magnetic duality rotations, $\mathrm{F}\ensuremath{\rightarrow}\mathrm{F}\mathrm{cos}\ensuremath{\theta}+^{\ensuremath{\star}}\mathrm{F}\mathrm{sin}\ensuremath{\theta}$. These transformations are indeed a symmetry of the theory in the Noether sense. The associated constant of motion is the difference in the intensity between self-dual and anti-self-dual components of the electromagnetic field or, equivalently, the difference between the right and left circularly polarized components. This conservation law holds even if the electromagnetic field interacts with an arbitrary classical gravitational background.…
CHIRAL ANOMALY IN ASHTEKAR'S APPROACH TO CANONICAL GRAVITY
1998
The Dirac equation in Riemann–Cartan spacetimes with torsion is reconsidered. As is well-known, only the axial covector torsion A, a one-form, couples to massive Dirac fields. Using diagrammatic techniques, we show that besides the familiar Riemannian term only the Pontrjagin type four-form dA ∧ dA does arise additionally in the chiral anomaly, but not the Nieh–Yan term d* A, as has been claimed recently. Implications for cosmic strings in Einstein–Cartan theory as well as for Ashtekar's canonical approach to quantum gravity are discussed.
How diffusivity, thermocline and incident light intensity modulate the dynamics of Deep Chlorophyll Maximum in Tyrrhenian Sea
2015
During the last few years theoretical works have shed new light and proposed new hypotheses on the mechanisms which regulate the spatio-temporal behaviour of phytoplankton communities in marine pelagic ecosystems. Despite this, relevant physical and biological issues, such as effects of the time- dependent mixing in the upper layer, competition between groups, and dynamics of non-stationary deep chlorophyll maxima, are still open questions. In this work, we analyze the spatio-temporal behaviour of five phytoplankton populations in a real marine ecosystem by using a one-dimensional reaction-diffusion-taxis model. The study is performed, taking into account the seasonal variations of environm…
Spatio-temporal dynamics of a planktonic system and chlorophyll distribution in a 2D spatial domain: matching model and data
2017
AbstractField data on chlorophyll distribution are investigated in a two-dimensional spatial domain of the Mediterranean Sea by using for phytoplankton abundances an advection-diffusion-reaction model, which includes real values for physical and biological variables. The study exploits indeed hydrological and nutrients data acquired in situ, and includes intraspecific competition for limiting factors, i.e. light intensity and phosphate concentration. As a result, the model allows to analyze how both the velocity field of marine currents and the two components of turbulent diffusivity affect the spatial distributions of phytoplankton abundances in the Modified Atlantic Water, the upper layer…
Dynamics of Two Picophytoplankton Groups in Mediterranean Sea: Analysis of the Deep Chlorophyll Maximum by a Stochastic Advection-Reaction-Diffusion …
2013
A stochastic advection-reaction-diffusion model with terms of multiplicative white Gaussian noise, valid for weakly mixed waters, is studied to obtain the vertical stationary spatial distributions of two groups of picophytoplankton, i.e., picoeukaryotes and Prochlorococcus, which account about for 60% of total chlorophyll on average in Mediterranean Sea. By numerically solving the equations of the model, we analyze the one-dimensional spatio-temporal dynamics of the total picophytoplankton biomass and nutrient concentration along the water column at different depths. In particular, we integrate the equations over a time interval long enough, obtaining the steady spatial distributions for th…
Resin adsorption as a means to enrich rare stilbenes and coumarin from pigeon pea leaves extracts
2011
Abstract In this study, resin adsorption as a means to enrich rare stilbenes cajaninstilbene acid (CSA) and longistyline C (LLC), and coumarin cajanuslactone (CL) from pigeon pea leaves was investigated. Among widely used twenty macroporous adsorption resins, NKA-9 resin presented higher adsorption capacity and desorption ratio in static tests. The adsorption kinetic model fitted better depended on types of compounds and pH values. The experimental adsorption data were better fitted to Langmuir isotherm (R2 0.921–0.991) than Freundlich isotherm (R2 0.753–0.988). In order to optimize the operating parameters for separating CSA, LLC and CL, dynamic adsorption and desorption tests were carried…
Gel chromatography
1968
Abstract The separation efficiency of gel chromatographic columns was investigated under a wide variety of experimental conditions. By use of reduced quantities it is possible to describe the separation efficiency for different gels and experimental conditions by a single equation. Deviations from this equation were found to be caused by an alteration of the diffusion coefficient within the gel with respect to the mobile phase. Factors governing the gel chromatography of p -oligophenylenes on poly(vinyl acetate) and poly(styrene) gels are generalized and discussed.
Gelchromatographische refraktionierung, 1. Ein verfahren zur korrektur von gelchromatogrammen
1979
A mathematical method is proposed for calculating the gel chromatogram w(v0) after correction with the instrument spreading function D(v, v0) and for calculating D(v,v0) using experimental data on the basis, that a gel chromatographic polymer fraction of the chromatogram e(v) is collected and injected again. The chromatogram of this fraction c(v) can be described by the integral equation: where v0 is the elution volume and v1 is the volume at which the fraction is collected. The solution of this equation simultaneously with Tung's equation by way of minimizing is suggested.
Ciberacoso escolar, ajuste psicosocial e ideación suicida en la adolescencia
2019
ABTSRACT Cyberbullying has become a growing social concern among the scientific community and in society in general. The consequences of cyberbullying for the victim are quite serious; many indicators of social maladjustment have been found, with suicide ideation being especially noteworthy. From this perspective, the main objective of this study was to analyze the relationships between cybervictimization and suicide ideation in adolescent victims of cyberbullying through the psychosocial maladjustment variables of loneliness, depressive symptomatology, perceived stress, and psychological distress. Participants in this study were 1,062 adolescents (547 boys, 515 girls), ranging in age from …