13,863 research outputs found
Dynamics of atomic spin-orbit-state wave packets produced by short-pulse laser photodetachment
We analyse the experiment by Hultgren et al. [Phys. Rev. A {\bf 87}, 031404
(2013)] on orbital alignment and quantum beats in coherently excited atomic
fine-structure manifolds produced by short-pulse laser photodetachment of
C, Si and Ge negative ions, and derive a formula that describes the
beats. Analysis of the experimental data enables us to extract the non-coherent
background contribution for each species, and indicates the need for a full
density matrix treatment of the problem
Comment on "Direct photodetachment of F by mid-infrared few-cycle femtosecond laser pulses"
Multiphoton detachment of F by strong few-cycle laser pulses was studied
by Shearer and Monteith using a Keldysh-type approach [Phys. Rev. A 88, 033415
(2013)]. We believe that this work contained errors in the calculation of the
detachment amplitude and photoelectron spectra. We describe the necessary
corrections to the theory and show that the results, in particular, the
interference features of the photoelectron spectra, appear noticeably
different.Comment: 9 pages, 4 figure
Two Wide Planetary-mass Companions to Solar-type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar-type stars occupy a curious region of
parameter space not obviously linked to binary star formation or solar system scale planet formation. These
companions provide insight into the extreme case of companion formation (either binary or planetary), and
due to their relative ease of observation when compared to close companions, they offer a useful template
for our expectations of more typical planets. We present the results from an adaptive optics imaging survey
for wide (~50–500 AU) companions to solar-type stars in Upper Scorpius. We report one new discovery of a
~14 M_J companion around GSC 06214−00210and confirm that the candidate planetary-mass companion 1RXS
J160929.1−210524 detected by Lafrenière et al. is in fact comoving with its primary star. In our survey, these
two detections correspond to ~4% of solar-type stars having companions in the 6–20 M_J mass and ~200–500 AU
separation range. This figure is higher than would be expected if brown dwarfs and planetary-mass companions
were drawn from an extrapolation of the binary mass function. Finally, we discuss implications for the formation
of these objects
Cost comparison of asthma treatments in 12-week study : caution about matching and short observational follow-up
This review was funded by Observational and Pragmatic Research Institute Pte Ltd.Peer reviewedPublisher PD
Sagittal Subtalar and Talocrural Joint Assessment During Ambulation With Controlled Ankle Movement (CAM) Boots
Background: The purpose of the current study was to determine sagittal plane talocrural and subtalar kinematic differences between barefoot and controlled ankle movement (CAM) boot walking. This study used fluoroscopic images to determine talar motion relative to tibia and calcaneal motion relative to talus.
Methods: Fourteen male subjects (mean age 24.1 ± 3.5 years) screened for normal gait were tested. A fluoroscopy unit was used to collect images at 200 Hz during stance. Sagittal motion of the talocrural and subtalar joints were analyzed barefoot and within short and tall CAM boots.
Results: Barefoot talocrural mean maximum plantar and dorsiflexion were 9.2 ± 5.4 degrees and −7.5 ± 7.4 degrees, respectively; short CAM boot mean maximum plantar and dorsiflexion were 3.2 ± 4.0 degrees and −4.8 ± 10.2 degrees, respectively; and tall CAM boot mean maximum plantar and dorsiflexion were −0.2 ± 3.5 degrees and −2.4 ± 5.1 degrees, respectively. Talocrural mean range of motion (ROM) decreased from barefoot (16.7 ± 5.1 degrees) to short CAM boot (8.0 ± 4.9 degrees) to tall CAM boot (2.2 ± 2.5 degrees). Subtalar mean maximum plantarflexion angles were 5.3 ± 5.6 degrees for barefoot walking, 4.1 ± 5.9 degrees for short CAM boot walking, and 3.0 ± 4.7 degrees for tall CAM boot walking. Mean minimum subtalar plantarflexion angles were 0.7 ± 3.2 degrees for barefoot walking, 0.7 ± 2.9 degrees for short CAM boot walking, and 0.1 ± 4.8 degrees for tall CAM boot walking. Subtalar mean ROM decreased from barefoot (4.6 ± 3.9 degrees) to short CAM boot (3.4 ± 3.8 degrees) to tall CAM boot (2.9 ± 2.6 degrees).
Conclusion: Tall and short CAM boot intervention was shown to limit both talocrural and subtalar motion in the sagittal plane during ambulation. The greatest reductions were seen with the tall CAM boot, which limited talocrural motion by 86.8% and subtalar motion by 37.0% compared to barefoot. Short CAM boot intervention reduced talocrural motion by 52.1% and subtalar motion by 26.1% compared to barefoot.
Clinical Relevance: Both short and tall CAM boots reduced talocrural and subtalar motion during gait. The short CAM boot was more convenient to use, whereas the tall CAM boot more effectively reduced motion. In treatments requiring greater immobilization of the talocrural and subtalar joints, the tall CAM boot should be considered
Stability of Filters for the Navier-Stokes Equation
Data assimilation methodologies are designed to incorporate noisy
observations of a physical system into an underlying model in order to infer
the properties of the state of the system. Filters refer to a class of data
assimilation algorithms designed to update the estimation of the state in a
on-line fashion, as data is acquired sequentially. For linear problems subject
to Gaussian noise filtering can be performed exactly using the Kalman filter.
For nonlinear systems it can be approximated in a systematic way by particle
filters. However in high dimensions these particle filtering methods can break
down. Hence, for the large nonlinear systems arising in applications such as
weather forecasting, various ad hoc filters are used, mostly based on making
Gaussian approximations. The purpose of this work is to study the properties of
these ad hoc filters, working in the context of the 2D incompressible
Navier-Stokes equation. By working in this infinite dimensional setting we
provide an analysis which is useful for understanding high dimensional
filtering, and is robust to mesh-refinement. We describe theoretical results
showing that, in the small observational noise limit, the filters can be tuned
to accurately track the signal itself (filter stability), provided the system
is observed in a sufficiently large low dimensional space; roughly speaking
this space should be large enough to contain the unstable modes of the
linearized dynamics. Numerical results are given which illustrate the theory.
In a simplified scenario we also derive, and study numerically, a stochastic
PDE which determines filter stability in the limit of frequent observations,
subject to large observational noise. The positive results herein concerning
filter stability complement recent numerical studies which demonstrate that the
ad hoc filters perform poorly in reproducing statistical variation about the
true signal
Optimizing photon indistinguishability in the emission from incoherently-excited semiconductor quantum dots
Most optical quantum devices require deterministic single-photon emitters.
Schemes so far demonstrated in the solid state imply an energy relaxation which
tends to spoil the coherent nature of the time evolution, and with it the
photon indistinguishability. We focus our theoretical investigation on
semiconductor quantum dots embedded in microcavities. Simple and general
relations are identified between the photon indistinguishability and the
collection efficiency. The identification of the key parameters and of their
interplay provides clear indications for the device optimization
Teaching Money Literacy in a Positive Youth Development Program: The Project P.A.T.H.S. in Hong Kong
In view of the high impact of materialistic orientation among children and adolescents, financial educational programs are provided as preventive measures. Without a clear framework, it is impossible to evaluate these programs. The goals of this paper are threefold. Firstly, the phenomena related to adolescent materialistic orientation and its associated problems in Hong Kong are examined. Secondly, the concept of financial education as a preventive measure is reviewed. Both board and narrow definitions of money literacy are examined. A framework on money literacy for children and adolescents as a founding stone for financial education is proposed. The framework finds its support from a typology proposed by the authors and results from an integration of research findings on dimensions of the concepts of money and success. Finally, curriculum units for Grades 7 to 9 students in a positive youth development program (the Project P.A.T.H.S.) are developed using the framework
2MASS Studies of Differential Reddening Across Three Massive Globular Clusters
J, H, and K_S band data from the Two Micron All-Sky Survey (2MASS) are used
to study the effects of differential reddening across the three massive
Galactic globular clusters Omega Centauri, NGC 6388, and NGC 6441. Evidence is
found that variable extinction may produce false detections of tidal tails
around Omega Centauri. We also investigate what appears to be relatively strong
differential reddening towards NGC 6388 and NGC 6441, and find that
differential extinction may be exaggerating the need for a metallicity spread
to explain the width of the red giant branches for these two clusters. Finally,
we consider the implications of these results for the connection between
unusual, multipopulation globular clusters and the cores of dwarf spheroidal
galaxies (dSph).Comment: 40 pages, 14 figures. Accepted for publication in Oct. 2003 A
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