264 research outputs found
Approaching the Heisenberg limit in an atom laser
We present experimental and theoretical results showing the improved beam quality and reduced divergence
of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We
show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled
atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater
than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can
produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces
them, typically a factor of 1.3 above the Heisenberg limit
Investigation and comparison of multi-state and two-state atom laser output-couplers
We investigate the spatial structure and temporal dynamics created in a
Bose-Einstein condensate (BEC) by radio-frequency (RF) atom laser
output-couplers using a one-dimensional mean-field model. We compare the
behavior of a `pure' two-state atom laser to the multi-level systems
demonstrated in laboratories. In particular, we investigate the peak
homogeneous output flux, classical fluctuations in the beam and the onset of a
bound state which shuts down the atom laser output.Comment: 9 pages, 8 figure
Directly Imaged L-T Transition Exoplanets in the Mid-Infrared
Gas-giant planets emit a large fraction of their light in the mid-infrared
(3m), where photometry and spectroscopy are critical to our
understanding of the bulk properties of extrasolar planets. Of particular
importance are the L and M-band atmospheric windows (3-5m), which are the
longest wavelengths currently accessible to ground-based, high-contrast
imagers. We present binocular LBT AO images of the HR 8799 planetary system in
six narrow-band filters from 3-4m, and a Magellan AO image of the 2M1207
planetary system in a broader 3.3m band. These systems encompass the five
known exoplanets with luminosities consistent with LT transition
brown dwarfs. Our results show that the exoplanets are brighter and have
shallower spectral slopes than equivalent temperature brown dwarfs in a
wavelength range that contains the methane fundamental absorption feature
(spanned by the narrowband filters and encompassed by the broader 3.3m
filter). For 2M1207 b, we find that thick clouds and non-equilibrium chemistry
caused by vertical mixing can explain the object's appearance. For the HR 8799
planets, we present new models that suggest the atmospheres must have patchy
clouds, along with non-equilibrium chemistry. Together, the presence of a
heterogeneous surface and vertical mixing presents a picture of dynamic
planetary atmospheres in which both horizontal and vertical motions influence
the chemical and condensate profiles.Comment: Accepted to Ap
On the Morphology and Chemical Composition of the HR 4796A Debris Disk
[abridged] We present resolved images of the HR 4796A debris disk using the
Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the
disk at 0.77 \microns, 0.91 \microns, 0.99 \microns, 2.15 \microns, 3.1
\microns, 3.3 \microns, and 3.8 \microns. We find that the deprojected center
of the ring is offset from the star by 4.761.6 AU and that the deprojected
eccentricity is 0.060.02, in general agreement with previous studies. We
find that the average width of the ring is 14, also comparable to
previous measurements. Such a narrow ring precludes the existence of
shepherding planets more massive than \about 4 \mj, comparable to hot-start
planets we could have detected beyond \about 60 AU in projected separation.
Combining our new scattered light data with archival HST/STIS and HST/NICMOS
data at \about 0.5-2 \microns, along with previously unpublished Spitzer/MIPS
thermal emission data and all other literature thermal data, we set out to
constrain the chemical composition of the dust grains. After testing 19
individual root compositions and more than 8,400 unique mixtures of these
compositions, we find that good fits to the scattered light alone and thermal
emission alone are discrepant, suggesting that caution should be exercised if
fitting to only one or the other. When we fit to both the scattered light and
thermal emission simultaneously, we find mediocre fits (reduced chi-square
\about 2). In general, however, we find that silicates and organics are the
most favored, and that water ice is usually not favored. These results suggest
that the common constituents of both interstellar dust and solar system comets
also may reside around HR 4796A, though improved modeling is necessary to place
better constraints on the exact chemical composition of the dust.Comment: Accepted to ApJ on October 27, 2014. 21 pages, 12 figures, 4 table
Resolving the Dusty Circumstellar Structure of the Enigmatic Symbiotic Star CH Cygni with the MMT Adaptive Optics System
We imaged the symbiotic star CH Cyg and two PSF calibration stars using the
unique 6.5m MMT deformable secondary adaptive optics system. Our
high-resolution (FWHM=0.3"), very high Strehl (98%+-2%) mid-infrared (9.8 and
11.7 um) images of CH Cyg allow us to probe finer length scales than ever
before for this object. CH Cyg is significantly extended compared to our
unresolved PSF calibration stars (Mu UMa and Alpha Her) at 9.8 and 11.7 um. We
estimated the size of the extension by convolving a number of simple Gaussian
models with the Mu UMa PSF and determining which model provided the best fit to
the data. Adopting the Hipparcos distance for this object of 270 pc, we found a
nearly Gaussian extension with a FWHM at 9.8 um of ~40.5+-2.7 AU (0.15+-0.01")
and a FWHM at 11.7 um of 45.9+-2.7 AU (0.17+-0.01"). After subtracting out the
Gaussian component of the emission (convolved with our PSF), we found a faint
\~0.7" asymmetric extension which peaks in flux ~0.5" north of the stars. This
extension is roughly coincident with the northern knotlike feature seen in HST
WFPC2 images obtained in 1999.Comment: 18 pages, 7 figures, accepted by the Astrophysical Journa
Scaling of Dirac Fermions and the WKB approximation
We discuss a new method for obtaining the WKB approximation to the Dirac
equation with a scalar potential and a time-like vector potential. We use the
WKB solutions to investigate the scaling behavior of a confining model for
quark-hadron duality. In this model, a light quark is bound to a heavy di-quark
by a linear scalar potential. Absorption of virtual photons promotes the quark
to bound states. The analog of the parton model for this case is for a virtual
photon to eject the bound, ground-state quark directly into free continuum
states. We compare the scaling limits of the response functions for these two
transitions
Empowering Responsible Online Gambling by Real-time Persuasive Information Systems
Online gambling, unlike other mediums of problem- atic and addictive behaviours, such as tobacco and alcohol, offers unprecedented opportunities for building information systems that are able to monitor and understand a user’s behaviour in real-time and adapt persuasive messages and interactions that would fit their personal profile and usage context. Online gambling industry usually provides Application Programming Interfaces (APIs) meant mainly to enable third-party applications to network with their gambling services and enhance a user’s gambling experience. In this industrial practice and experience paper, we advocate that such API’s can also be used to retrieve gamblers’ online data, such as browsing and betting history, promotions and available offers and use it to build more intel- ligent and proactive responsible gambling information systems. We report on our industrial experience in this field and make the argument that data available for persuasive marketing and usability should, under specific usage conditions, also be made available for responsible gambling information systems. This principle would provide equal opportunities for both directions. We discuss the psychological foundations of our proposed solution and the risks and challenges typically found when building such a software-assisted intervention, persuasion and emotion regulation technology. We also shed light on its potential implications from the perspectives of social corporate responsibility and data protection. We finally propose a conceptual architecture to demonstrate our vision and explain how it can be implemented. In the wider context, the paper is meant to provide insights on building behavioural awareness and regulation information systems in relation to problematic digital media usage
Mid-Infrared Imaging of the Post-AGB Star AC Herculis with the MMT Adaptive Optics System
We utilized the MMT's unique deformable secondary adaptive optics system to
produce high-resolution (FWHM=0.3"), very high Strehl mid-infrared (9.8, 11.7 &
18 micron) images of the post-AGB star AC Her. The very high (98+/-2%) Strehls
achieved with Mid-IR AO led naturally to an ultra-stable PSF independent of
airmass, seeing, or location on the sky. We find no significant difference
between AC Her's morphology and our unresolved PSF calibration stars (mu UMa &
alpha Her) at 9.8, 11.7, & 18 microns. Our current observations do not confirm
any extended Mid-IR structure around AC Her. These observations are in conflict
with previously reported Keck (seeing-limited) 11.7 and 18 micron images which
suggested the presence of a resolved ~0.6" edge-on circumbinary disk. We
conclude that AC Her has no extended Mid-IR structure on scales greater than
0.2" (R<75 AU). These first results of Mid-IR AO science are very encouraging
for future high accuracy Mid-IR imaging with this technique.Comment: To appear in the November 20, 2003 issue of the Astrophysical Journal
Letters. The preprint has 7 pages and 3 figures (one in color; but prints OK
in B&W
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