4,169 research outputs found
Quantum interference initiated super- and subradiant emission from entangled atoms
We calculate the radiative characteristics of emission from a system of
entangled atoms which can have a relative distance larger than the emission
wavelength. We develop a quantum multipath interference approach which explains
both super- and subradiance though the entangled states have zero dipole
moment. We derive a formula for the radiated intensity in terms of different
interfering pathways. We further show how the interferences lead to directional
emission from atoms prepared in symmetric W-states. As a byproduct of our work
we show how Dicke's classic result can be understood in terms of interfering
pathways. In contrast to the previous works on ensembles of atoms, we focus on
finite numbers of atoms prepared in well characterized states.Comment: 10 pages, 8 figures, 2 Table
Modeling Multi-Wavelength Stellar Astrometry. I. SIM Lite Observations of Interacting Binaries
Interacting binaries consist of a secondary star which fills or is very close
to filling its Roche lobe, resulting in accretion onto the primary star, which
is often, but not always, a compact object. In many cases, the primary star,
secondary star, and the accretion disk can all be significant sources of
luminosity. SIM Lite will only measure the photocenter of an astrometric
target, and thus determining the true astrometric orbits of such systems will
be difficult. We have modified the Eclipsing Light Curve code (Orosz &
Hauschildt 2000) to allow us to model the flux-weighted reflex motions of
interacting binaries, in a code we call REFLUX. This code gives us sufficient
flexibility to investigate nearly every configuration of interacting binary. We
find that SIM Lite will be able to determine astrometric orbits for all
sufficiently bright interacting binaries where the primary or secondary star
dominates the luminosity. For systems where there are multiple components that
comprise the spectrum in the optical bandpass accessible to SIM Lite, we find
it is possible to obtain absolute masses for both components, although
multi-wavelength photometry will be required to disentangle the multiple
components. In all cases, SIM Lite will at least yield accurate inclinations,
and provide valuable information that will allow us to begin to understand the
complex evolution of mass-transferring binaries. It is critical that SIM Lite
maintains a multi-wavelength capability to allow for the proper deconvolution
of the astrometric orbits in multi-component systems.Comment: 12 pages, 6 figures, 6 tables. Accepted for publication in the
Astrophysical Journa
Ab Initio Calculations of the Walls Shear Strength of Carbon Nanotubes
The dependence of the energy of interwall interaction in double-walled carbon
nanotubes (DWNT) on the relative position of walls has been calculated using
the density functional method. This dependence is used to evaluate forces that
are necessary for the relative telescopic motion of walls and to calculate the
shear strength of DWNT for the relative sliding of walls along the nanotube
axis and for their relative rotation about this axis. The possibility of
experimental verification of the obtained results is discussed.Comment: 4 pages, 1 figur
Microwave emission from a crystal of molecular magnets -- The role of a resonant cavity
We discuss the effects caused by a resonant cavity around a sample of a
magnetic molecular crystal (such as Mn-Ac), when a time dependent
external magnetic field is applied parallel to the easy axis of the crystal. We
show that the back action of the cavity field on the sample significantly
increases the possibility of microwave emission. This radiation process can be
supperradiance or a maser-like effect, depending on the strength of the
dephasing. Our model provides further insight to the theoretical understanding
of the bursts of electromagnetic radiation observed in recent experiments
accompanying the resonant quantum tunneling of magnetization. The experimental
findings up to now can all be explained as being a maser effect rather than
superradiance. The results of our theory scale similarly to the experimental
findings, i.e., with increasing sweep rate of the external magnetic field, the
emission peaks are shifted towards higher field values.Comment: 12 pages, 6 figures. To appear in Phys. Rev.
Localized states in strong magnetic field: resonant scattering and the Dicke effect
We study the energy spectrum of a system of localized states coupled to a 2D
electron gas in strong magnetic field. If the energy levels of localized states
are close to the electron energy in the plane, the system exhibits a kind of
collective behavior analogous to the Dicke effect in optics. The latter
manifests itself in ``trapping'' of electronic states by localized states. At
the same time, the electronic density of states develops a gap near the
resonance. The gap and the trapping of states appear to be complementary and
reflect an intimate relation between the resonant scattering and the Dicke
effect. We reveal this relation by presenting the exact solution of the problem
for the lowest Landau level. In particular, we show that in the absence of
disorder the system undergoes a phase transition at some critical concentration
of localized states.Comment: 28 pages + 9 fig
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Study of Different Aging Conditions for Analysis of Microstructure and Mechanical Properties of F357 Alloy Fabricated in LPBF Printer
Aluminum F357 is a widely used material for casting in aerospace and additive manufacturing
industry. Heat treatments are commonly applied to some aluminum alloys to modify its
properties. With a further study on the aging and performance of the F357 with 3D printing
technology, several industries benefit of this, military, automotive and aerospace are some
examples, because the numerous components casted in service. This work presents mechanical
properties of F357 specimens fabricated with EOS technology and subjected to heat treatments.
Heat treatments conditions were applied to tensile specimens and tested. Furthermore, the
specimens were subjected to artificial thermal aging for 100 h and 1000 h at two different
temperatures (285 ºF and 350 ºF), and their mechanical properties were also determined. Finally,
remarks on the comparison between the heat treatments and the effect of thermal aging on the
microstructures and mechanical properties of the specimens will be presented.Mechanical Engineerin
Notes
Notes by Benedict R. Danko, Patrick F. Coughlin, William J. O\u27Connor, John E. Lindberg, Lawrence S. May, Jr., Arthur L. Beaudette, and Mark Harry Berens
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