2,694 research outputs found
Turbulent Formation of Interstellar Structures and the Connection Between Simulations and Observations
I review recent results derived from numerical simulations of the turbulent
interstellar medium (ISM), in particular concerning the nature and formation of
turbulent clouds, methods for comparing the structure in simulations and
observations, and the effects of projection of three-dimensional structures
onto two dimensions. Clouds formed as turbulent density fluctuations are
probably not confined by thermal pressure, but rather their morphology may be
determined by the large-scale velocity field. Also, they may have shorter
lifetimes than normally believed, as the large-scale turbulent modes have
larger associated velocities than the clouds' internal velocity dispersions.
Structural characterization algorithms have started to distinguish the best
fitting simulations to a particular observation, and have opened several new
questions, such as the nature of the observed line width-size relation and of
the relation between the structures seen in channel maps and the true spatial
distribution of the density and velocity fields. The velocity field apparently
dominates the morphology seen in intensity channel maps, at least in cases when
the density field exhibits power spectra steep enough. Furthermore, the
selection of scattered fluid parcels along the line of sight (LOS) by their
LOS-velocity inherent to the construction of spectroscopic data may introduce
spurious small-scale structure in high spectral resolution channel maps.Comment: 15 pages, no figures. To appear in the Proceedings of "The Chaotic
Universe", Roma/Pescara, Italy, 1-5 Feb. 1999, eds. V. Gurzadyan and L.
Bertone. Uses included .cls fil
Classical Emergence of Intrinsic Spin-Orbit Interaction of Light at the Nanoscale
Traditionally, in macroscopic geometrical optics intrinsic polarization and
spatial degrees of freedom of light can be treated independently. However, at
the subwavelength scale these properties appear to be coupled together, giving
rise to the spin-orbit interaction (SOI) of light. In this work we address
theoretically the classical emergence of the optical SOI at the nanoscale. By
means of a full-vector analysis involving spherical vector waves we show that
the spin-orbit factorizability condition, accounting the mutual influence
between the amplitude (spin) and phase (orbit), is fulfilled only in the
far-field limit. On the other side, in the near-field region, an additional
relative phase introduces an extra term that hinders the factorization and
reveals an intricate dynamical behavior according to the SOI regime. As a
result, we find a suitable theoretical framework able to capture analytically
the main features of intrinsic SOI of light. Besides allowing for a better
understanding into the mechanism leading to its classical emergence at the
nanoscale, our approach may be useful in order to design experimental setups
that enhance the response of SOI-based effects.Comment: 10 pages, 5 figure
Coloquio de La Habana: "Encuentro sobre la deuda externa de América Latina y el Caribe". Argentina
El problema de la deuda externa viene ocupando, en estos últimos años, un lugar central en el escenario económico y político de América Latina. El dramatismo de la situación ha sido subrayado repetidamente, y los indicadores que reflejan el comportamiento negativo del producto, la ocupación, la inversión, las presiones inflacionarias, los salarios reales, el drenaje de reservas internacionales y todas las demás magnitudes macroeconómicas relevantes, dan testimonio fehaciente de la gravedad de la crisis, en la que el peso abrumador de la deuda es el principal elemento determinante
Near-Field Directionality Beyond the Dipole Approximation: Electric Quadrupole and Higher-Order Multipole Angular Spectra
Within the context of spin-related optical phenomena, the near-field
directionality is generally understood from the quantum spin Hall effect of
light, according to which the transverse spin of surface or guided modes is
locked to the propagation direction. So far, most previous works have been
focused on the spin properties of circularly polarized dipolar sources.
However, in near-field optics, higher-order multipole sources (e.g.,
quadrupole, octupole, and so on) might become relevant, so a more in-depth
formulation would be highly valuable. Building on the angular spectrum
representation, we provide a general, analytical, and ready-to-use treatment in
order to address the near-field directionality of any multipole field,
particularizing to the electric quadrupole case. Besides underpinning and
upgrading the current framework on spin-dependent directionality, our results
may open up new perspectives for engineering light-matter coupling at the
nanoscale.Comment: 7 pages, 2 figures. Supplemental Material (19 pages). Supplemental
tools (calculator of angular spectra and animation) available at
https://doi.org/10.5281/zenodo.267790
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