18,309 research outputs found
Spinning jets
A fluid jet with a finite angular velocity is subject to centripetal forces
in addition to surface tension forces. At fixed angular momentum, centripetal
forces become large when the radius of the jet goes to zero. We study the
possible importance of this observation for the pinching of a jet within a
slender jet model. A linear stability analysis shows the model to break down at
low viscosities. Numerical simulations indicate that angular momentum is
expelled from the pinch region so fast that it becomes asymptotically
irrelevant in the limit of the neck radius going to zero
Nuclear shadowing and prompt photons at relativistic hadron colliders
The production of prompt photons at high energies provides a direct probe of
the dynamics of the strong interactions. In particular, one expect that it
could be used to constrain the behavior of the nuclear gluon distribution in
and collisions. In this letter we investigate the influence of
nuclear effects in the production of prompt photons and estimate the transverse
momentum dependence of the nuclear ratios and at RHIC and LHC
energies. We demonstrate that the study of these observables can be useful to
determine the magnitude of the shadowing and antishadowing effects in the
nuclear gluon distribution.Comment: 4 pages, 3 figures. Version to be published in PR
On the stabilization of ion sputtered surfaces
The classical theory of ion beam sputtering predicts the instability of a
flat surface to uniform ion irradiation at any incidence angle. We relax the
assumption of the classical theory that the average surface erosion rate is
determined by a Gaussian response function representing the effect of the
collision cascade and consider the surface dynamics for other
physically-motivated response functions. We show that although instability of
flat surfaces at any beam angle results from all Gaussian and a wide class of
non-Gaussian erosive response functions, there exist classes of modifications
to the response that can have a dramatic effect. In contrast to the classical
theory, these types of response render the flat surface linearly stable, while
imperceptibly modifying the predicted sputter yield vs. incidence angle. We
discuss the possibility that such corrections underlie recent reports of a
``window of stability'' of ion-bombarded surfaces at a range of beam angles for
certain ion and surface types, and describe some characteristic aspects of
pattern evolution near the transition from unstable to stable dynamics. We
point out that careful analysis of the transition regime may provide valuable
tests for the consistency of any theory of pattern formation on ion sputtered
surfaces
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