942 research outputs found
Revealing the Young Starburst in Haro 3 with Radio and Infrared Imaging
The Wolf-Rayet galaxy Haro 3 (Mrk 35, NGC 3353) was observed at the near-IR
and radio wavelengths as part of ongoing program to study the earliest stages
of starbursts. These observations confirm that the current episode of star
formation is dominated by a single region (region A). While there are knots of
recent (~10 Myr) star formation outside of region A, the sources of ionizing
radiation as observed in both radio and Br-gamma observations are almost
exclusively associated with region A. The derived ionizing flux implies a star
formation rate of ~0.6 solar masses per year localized within a radius of ~0.1
kpc. A comparison with observations from HST indicates that one or more of the
star clusters in region A are optically obscured. The star clusters in region A
have ages at least as young as ~5 Myr, and possibly as young as ~0.1 Myr. The
star cluster that appears to be the youngest also exhibits a near-IR excess in
its colors, possibly indicating natal dust in very close proximity to the
ionizing stars. The difference between optical- and radio-determined ionizing
fluxes as well as the near-IR colors indicate an average extinction value of
A_V ~2.5 in region A. The total stellar mass associated with the current
starburst in region A is inferred from both the near-IR and radio observations
to be ~10^6 solar masses. The other main stellar concentrations observed in the
near-IR (Regions B1 and B2) are somewhat older than region A, with ages ~8-10
Myr, and the near-IR observations indicate they have stellar masses of ~8x10^4
and ~2x10^4 solar masses, respectively.Comment: 17 pages, 3 figures, to appear in AJ August 200
Dynamical properties across a quantum phase transition in the Lipkin-Meshkov-Glick model
It is of high interest, in the context of Adiabatic Quantum Computation, to
better understand the complex dynamics of a quantum system subject to a
time-dependent Hamiltonian, when driven across a quantum phase transition. We
present here such a study in the Lipkin-Meshkov-Glick (LMG) model with one
variable parameter. We first display numerical results on the dynamical
evolution across the LMG quantum phase transition, which clearly shows a
pronounced effect of the spectral avoided level crossings. We then derive a
phenomenological (classical) transition model, which already shows some
closeness to the numerical results. Finally, we show how a simplified quantum
transition model can be built which strongly improve the classical approach,
and shed light on the physical processes involved in the whole LMG quantum
evolution. From our results, we argue that the commonly used description in
term of Landau-Zener transitions is not appropriate for our model.Comment: 7 pages, 5 figures; corrected reference
Thermal Excitation of Broadband and Long-range Surface Waves on SiO 2 Submicron Films
We detect thermally excited surfaces waves on a submicron SiO 2 layer,
including Zenneck and guided modes in addition to Surface Phonon Polaritons.
The measurements show the existence of these hybrid thermal-electromagnetic
waves from near-(2.7 m) to far-(11.2 m) infrared. Their propagation
distances reach values on the order of the millimeter, several orders of
magnitude larger than on semi-infinite systems. These two features, spectral
broadness and long range propagation, make these waves good candidates for
near-field applications both in optics and thermics due to their dual nature.Comment: Applied Physics Letters, American Institute of Physics, 201
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