4,737 research outputs found
Liner radius fluctuations in a high-gain Cherenkov free-electron laser
Phase shifts in the propagating electromagnetic field of a Cherenkov free-electron laser (CFEL) can affect its gain. The phase velocity of an electromagnetic wave varies, for example, when the lined waveguide is inhomogeneous along its length. In this paper, we study quantitatively the saturated power of a particular CFEL at both weak and strong electron-beam pumping when the inner radius of the liner contains fluctuations along the waveguide. We show that the gain bandwidth of the CFEL is substantially broadened when the CFEL is pumped with a high-current beam. We also show that the design of a CFEL needs to include optimization with respect to sensitivity to liner fluctuations, especially for weakly pumped CFELs, that is, CFELs that use a low-current electron-beam density. This optimization can be relaxed for more strongly pumped CFELs
Diffusive Transport Enhanced by Thermal Velocity Fluctuations
We study the contribution of advection by thermal velocity fluctuations to
the effective diffusion coefficient in a mixture of two indistinguishable
fluids. The enhancement of the diffusive transport depends on the system size L
and grows as \ln(L/L_0) in quasi two-dimensional systems, while in three
dimensions it scales as L_0^{-1}-L^{-1}, where L_0 is a reference length. The
predictions of a simple fluctuating hydrodynamics theory are compared to
results from particle simulations and a finite-volume solver and excellent
agreement is observed. Our results conclusively demonstrate that the nonlinear
advective terms need to be retained in the equations of fluctuating
hydrodynamics when modeling transport in small-scale finite systems.Comment: To appear in Phys. Rev. Lett., 201
Functional Resilience and Response to a Dietary Additive (Kefir) in Models of Foregut and Hindgut Microbial Fermentation In Vitro
Stability in gut ecosystems is an important area of study that impacts on the use of additives and is related with several pathologies. Kefir is a fermented milk drink made with a consortium of yeast and bacteria as a fermentation starter, of which the use as additive in companion and livestock animals has increased in the last few years. To investigate the effect of kefir milk on foregut and hindgut digestive systems, an in vitro approach was followed. Either rumen fluid or horse fecal contents were used as a microbial inoculate and the inclusion of kefir (fresh, autoclaved, or pasteurized) was tested. Gas production over 72 h of incubation was recorded and pH, volatile fatty acids (VFAs), lactate and ammonia concentration as well as lactic acid (LAB) and acetic acid bacteria, and yeast total numbers were also measured. Both direct and indirect (by subtracting their respective blanks) effects were analyzed and a multivariate analysis was performed to compare foregut and hindgut fermentation models. Addition of kefir boosted the fermentation by increasing molar concentration of VFAs and ammonia and shifting the Acetate to Propionate ratio in both models but heat processing techniques like pasteurization or autoclaving influenced the way the kefir is fermented and reacts with the present microbiota. In terms of comparison between both models, the foregut model seems to be less affected by the inclusion of Kefir than the hindgut model. In terms of variability in the response, the hindgut model appeared to be more variable than the foregut model in the way that it reacted indirectly to the addition of different types of kefirpublishersversionPeer reviewe
Comparación de métodos para modelar la aquiescencia en escalas multidimensionales parcialmente balanceadas.
Background: The inclusion of direct and reversed items in scales is a commonly-used strategy to control acquiescence bias. However, this is not enough to avoid the distortions produced by this response style in the structure of covariances and means of the scale in question. This simulation study provides evidence on the performance of two different procedures for modelling the influence of acquiescence bias on partially balanced multidimensional scales: a method based on exploratory factor analysis (EFA) with target rotation, and a method based on random intercept factor analysis (RIFA). Method: The independent variables analyzed in a simulation study were sample size, number of items per factor, balance of substantive loadings of direct and reversed items, size and heterogeneity of acquiescence loadings, and inter-factor correlation. Results: The RIFA method had better performance over most of the conditions, especially for the balanced conditions, although the variance of acquiescence factor loadings had a certain impact. In relation to the EFA method, it was severely affected by a low degree of balance. Conclusions: RIFA seems the most robust approach, but EFA also remains a good alternative for medium and fully balanced scales.Antecedentes: la
inclusión de Ãtems directos e inversos en escalas es una estrategia
comúnmente utilizada para controlar el sesgo de aquiescencia. No
obstante, esto es insufi ciente para evitar las distorsiones producidas por
este estilo de respuesta en la estructura de covarianzas y medias de la
escala. El presente estudio de simulación aporta evidencia sobre el
rendimiento de dos procedimientos para controlar la infl uencia del sesgo
de aquiescencia en escalas multidimensionales parcialmente balanceadas:
un método basado en análisis factorial exploratorio con rotación target
(EFA), y un método basado en el análisis factorial confi rmatorio con
intercepto aleatorio (RIFA). Método: las variables independientes del
estudio de simulación fueron: tamaño muestral, número de Ãtems por
factor, balanceo de los pesos sustantivos de los Ãtems directos e inversos,
tamaño y heterogeneidad de los pesos en aquiescencia, y correlación
entre factores. Resultados: el método RIFA tiene mejor funcionamiento
en general, especialmente para las condiciones balanceadas, aunque la
varianza de los pesos de aquiescencia tuvo impacto en su rendimiento.
El método EFA se ve principalmente afectado en la situación de bajo
balanceo. Conclusiones: el RIFA parece la aproximación más robusta,
aunque el EFA se mantiene como una alternativa a considerar para escalas
con balanceo medio o completoThis research was partially supported by Ministerio de Ciencia,
Innovación y Universidades, Spain (Grant PSI2017-85022-P),
European Social Fund, and Cátedra de Modelos y Aplicaciones
Psicométricas (Instituto de IngenierÃa del Conocimiento and
Autonomous University of Madrid)
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