14,706 research outputs found
Unconditional jetting
Capillary jetting of a fluid dispersed into another immiscible phase is
usually limited by a critical Capillary number, a function of the Reynolds
number and the fluid properties ratios. Critical conditions are set when the
minimum spreading velocity of small perturbations along the jet
(marginal stability velocity) is zero. Here we identify and describe
parametrical regions of high technological relevance, where and the
jet flow is always supercritical independently of the dispersed liquid flow
rate: within these relatively broad regions, the jet does not undergo the usual
dripping-jetting transition, so that either the jet can be made arbitrarily
thin (yielding droplets of any imaginably small size), or the issued flow rate
can be made arbitrarily small. In this work, we provide illustrative analytical
studies of asymptotic cases for both negligible and dominant inertia forces. In
this latter case, requiring a non-zero jet surface velocity, axisymmetric
perturbation waves ``surf'' downstream for all given wave numbers while the
liquid bulk can remain static. In the former case (implying small Reynolds
flow) we found that the jet profile small slope is limited by a critical value;
different published experiments support our predictions.Comment: Submitted first (24-August-2008) to Physics of Fluids, withdrawn from
that journal on 6-April-2008, and submitted to Physical Review E the same da
The scaling of exploding liquid jets under intense X-ray pulses
A general scaling of the evolution of an exploding liquid jet under an ultra
short and intense X-ray pulse from a X-ray free electron laser (XFEL) is
proposed. A general formulation of the conservation of energy for blasts in
vacuum partially against a deformable object leads to a compact expression that
governs the evolution of the gap produced by the explosion. The theoretical
analysis contemplates two asymptotic stages for small and large times from the
initiation of the blast. A complete dimensional analysis of the problem and an
optimal collapse of experimental data reveal that the universal approximate
analytical solution proposed is in remarkable agreement with experiments
Scaling laws of top jet drop size and speed from bubble bursting including gravity and inviscid limit
Jet droplets from bubble bursting are determined by a limited parametrical
space: the liquid properties (surface tension, viscosity, and density), mother
bubble size and acceleration of gravity. Thus, the two resulting parameters
from dimensional analysis (usually, the Ohnesorge and Bond numbers, Oh and Bo)
completely define this phenomenon when both the trapped gas in the bubble and
the environment gas have negligible density. A detailed physical description of
the ejection process to model both the ejected droplet radius and its initial
launch speed is provided, leading to a scaling law including both Oh and Bo.
Two critical values of Oh determine two limiting situations: one (Oh=0.038)
is the critical value for which the ejected droplet size is minimum and the
ejection speed maximum, and the other (Oh=0.0045) is a new critical value
which signals when viscous effects vanish. Gravity effects (Bo) are
consistently introduced from energy conservation principles. The proposed
scaling laws produce a remarkable collapse of published experimental
measurements collected for both the ejected droplet radius and ejection speed.Comment: 14 pages, three figures, published in 2018 in Physical Review Fluid
Unemployment duration, unemployment benefits and recalls
We use administrative micro-data to investigate exits from unemployment of benefit recipients in Spain. Because the data allow us to distinguish between transitions to a new job and recall to the same employer, we apply a competing risks model with
observed and unobserved heterogeneity. We are also able to control for the type of
benefit received by the worker: insurance benefit or assistance benefit. We find
significant differences between the new job hazard and the recall hazard. Both hazard
rates increase around the time that insurance benefit elapses. We also find that when
larger firms recall unemployed workers they tend to do so faster than smaller firms. In
general, our results are consistent with predictions derived from search and implicit
contract models. They highlight the importance of taking into account the possibility of recall in the analysis of unemployment duration among unemployment benefit recipients
Completing constrained flavor violation: lepton masses, neutrinos and leptogenesis
Constrained flavor violation is a recent proposal for predicting the
down-quark Yukawa matrix in terms of those for up quarks and charged leptons.
We study the viability of CFV with respect to its predictions for the lepton
mass ratios, showing that this remains a challenge, and suggest some possible
means for improving this shortcoming. We then extend CFV to include neutrinos,
and show that it leads to interesting predictions for hierachical heavy
neutrinos, and leptogenesis dominated by decays of the second heaviest one ("N2
leptogenesis"), as well as the possibility of low-scale leptoquark-mediated
exotic decays.Comment: 13 pages, 7 figures; v.2: published version, reorganized and
clarified leptogenesis sectio
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