4,229 research outputs found
Minimal formulation of the linear spatial analysis of capillary jets: Validity of the two-mode approach
A rigorous and complete formulation of the linear evolution of harmonically stimulated
capillary jets should include infinitely many spatial modes to account for arbitrary exit
conditions [J. Guerrero et al., J. Fluid Mech. 702, 354 (2012)]. However, it is not rare to
find works in which only the downstream capillary dominant mode, the sole unstable one,
is retained, with amplitude determined by the jet deformation at the exit. This procedure
constitutes an oversimplification, unable to handle a flow rate perturbation without jet
deformation at the exit (the most usual conditions). In spite of its decaying behavior, the
other capillary mode (subdominant) must be included in what can be called a “minimal
linear formulation.” Deformation and mean axial velocity amplitudes at the jet exit are the
two relevant parameters to simultaneously find the amplitudes of both capillary modes.
Only once these amplitudes are found, the calculation of the breakup length may be
eventually simplified by disregarding the subdominant mode. Simple recipes are provided
for predicting the breakup length, which are checked against our own numerical simulations.
The agreement is better than in previous attempts in the literature. Besides, the limits of
validity of the linear formulation are explored in terms of the exit velocity amplitude, the
wave number, the Weber number, and the Ohnesorge number. Including the subdominant
mode extends the range of amplitudes for which the linear model gives accurate predictions,
the criterion for keeping this mode being that the breakup time must be shorter than a
given formula. It has been generally assumed that the shortest intact length happens for the
stimulation frequency with the highest growth rate. However, we show that this correlation
is not strict because the amplitude of the dominant mode has a role in the breakup process
and it depends on the stimulation frequency.Ministerio de Economía, Industria y Competitividad, Spain, under Contract No. FIS2014-25161Junta de Andalucía under Contract No. P11-FQM-791
¿Por qué Menesteo?: la entrada ateniense del Catálogo de las Naves (Ilíada, II, 546-556) y la edición pisistrática de los poemas homéricos
Sin resume
Intertemporal and spatial location of disposal facilities
The optimal capacities and locations of a sequence of landfills are studied, and the interactions between these characteristics are considered. Deciding the capacity of a landfill has some spatial implications since it affects the feasible region for the remaining landfills, and some temporal implications because the capacity determines the lifetime of the landfill and hence the moment of time when the next landfills should be constructed. Some general mathematical properties of the solution are provided and interpreted from an economic point of view. The resulting problem turns out to be non-convex and, therefore, it cannot be solved by conventional optimization techniques. Some global optimization methods are used to solve the problem in a particular case in order to illustrate how the solution depends on the parameter values
The Presence of Women in the Associations of Journalists in Spain
Las asociaciones de la prensa tienen por misión la defensa de la profesión periodística. En este trabajo analizamos estas instituciones desde la perspectiva de género, partiendo de la premisa de que una mayor
presencia de mujeres en las mismas podría favorecer la igualdad en la profesión. Para ello estudiamos la composición de sus juntas directivas y presidencia según el sexo y comprobamos si reproducen o no los
patrones que podemos encontrar en las empresas del sector. Las conclusiones a las que llegamos es que las mujeres están poco representadas en las juntas directivas, pero con un mayor equilibrio que en las empresas editoras, lo que nos hace atisbar una mejora en la igualdad en la profesión en un futuro próximo.Press associations have the task of defending the journalistic profession. In this paper we analyze these institutions from the perspective of gender, based on the premise that a greater presence of women in them could promote equality in the profession. To do so, we study the composition of their Boards of Directors and Chair by sex and verify if they reproduce the rules that we can find in the companies of the sector or not. The conclusion that we draw is that women are underrepresented on the Boards, but there is a better balance than in the press companies, which makes us discern an improvement in equality in the profession for the near future
Modelos de transposición de las Directivas 2002/91/CE y 2010/31/UE “Energy Performance Building Directive” en los Estados miembros de la UE. Consecuencias e implicaciones
Energy performance building directive? en los estados miembros de la UE. Consecuencias e implicaciones
Spatial modes in one-dimensional models for capillary jets
One-dimensional (1D) models are widely employed to simplify the analysis of axisymmetric capillary jets.
These models postulate that, for slender deformations of the free surface, the radial profile of the axial velocity
can be approximated as uniform (viscous slice, averaged, and Cosserat models) or parabolic (parabolic model). In
classical works on spatial stability analysis with 1D models, considerable misinterpretation was generated about
the modes yielded by each model. The already existing physical analysis of three-dimensional (3D) axisymmetric
spatial modes enables us to relate these 1D spatial modes to the exact 3D counterparts. To do so, we address the
surface stimulation problem, which can be treated as linear, by considering the effect of normal and tangential
stresses to perturb the jet. A Green’s function for a spatially local stimulation having a harmonic time dependence
provides the general formalism to describe any time-periodic stimulation. The Green’s function of this signaling
problem is known to be a superposition of the spatial modes, but in fact these modes are of fundamental nature,
i.e., not restricted to the surface stimulation problem. The smallness of the wave number associated with each
mode is the criterion to validate or invalidate the 1D approaches. The proposed axial-velocity profiles (planar or
parabolic) also have a remarkable influence on the outcomes of each 1D model.We also compare with the classical
3D results for (i) conditions for absolute instability, and (ii) the amplitude of the unstable mode resulting from
both normal and tangential surface stress stimulation. Incidentally, as a previous task, we need to re-deduce 1D
models in order to include eventual stresses of various possible origins (electrohydrodynamic, thermocapillary,
etc.) applied on the free surface, which were not considered in the previous general formulations.Gobierno de España FIS2011-25161Junta de Andalucía P11-FQM-791
Mortero acumulador de energía mediante parafina microencapsulada
En la construcción se puede almacenar calor a través de calor sensible y calor latente.
El almacenamiento por calor latente es menos utilizado en aplicaciones arquitectónicas
que el calor sensible, pero su capacidad de acumulación es mucho mayor. L
a utilización
de calor latente a través de materiales de cambio de fase (PCM), puede producir
mejoras en el acondicionamiento térmico y reducir el consumo de energía por
calefacción en los edificios. Por su posibilidad de uso en morteros de cemento, las
pa
rafinas microencapsuladas aparecen como una buena alternativa tecnológica dentro
de los materiales de construcción. Existe un grupo de problemas relacionados con el
cambio de comportamiento que experimenta el mortero dependiendo de las cantidades
incorpora
das de PCM microencapsulado. En el presente trabajo se expone su
aplicación a morteros de cemento en cantidades de 5, 10 y 20 %, y relaciones
agua/cemento de 0,50
;
0,70 y 0,90. Los resultados permiten ver los efectos en las
propiedades del mortero, observá
ndose disminución de resistencia y densidad, así
como también cambios en el comportamiento de mezclas en estado fresco de mortero
con PCM. Agregado en la mezcla, permite acumular mayores cantidades de energía sin
aumentar el espesor de la capa de mortero
Metric of a Slow Rotating Body with Quadrupole Moment from the Erez-Rosen Metric
A metric representing a slowly rotating object with quadrupole moment is
obtained using a perturbation method to include rotation into the weak limit of
the Erez-Rosen metric. This metric is intended to tackle relativistic
astrometry and gravitational lensing problems in which a quadrupole moment has
to be taken into account
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