3,166 research outputs found
Quantized Rabi Oscillations and Circular Dichroism in Quantum Hall Systems
The dissipative response of a quantum system upon a time-dependent drive can
be exploited as a probe of its geometric and topological properties. In this
work, we explore the implications of such phenomena in the context of
two-dimensional gases subjected to a uniform magnetic field. It is shown that a
filled Landau level exhibits a quantized circular dichroism, which can be
traced back to its underlying non-trivial topology. Based on selection rules,
we find that this quantized circular dichroism can be suitably described in
terms of Rabi oscillations, whose frequencies satisfy simple quantization laws.
Moreover, we discuss how these quantized dissipative responses can be probed
locally, both in the bulk and at the boundaries of the quantum Hall system.
This work suggests alternative forms of topological probes in quantum systems
based on circular dichroism.Comment: 7 pages, including 3 figures and Appendi
b anti-b Higgs production at the LHC: Yukawa corrections and the leading Landau singularity
At tree-level Higgs production in association with a b-quark pair proceeds
through the small Yukawa bottom coupling in the Standard Model. Even in the
limit where this coupling vanishes, electroweak one-loop effects, through the
top-Higgs Yukawa coupling in particular, can still trigger this reaction. This
contribution is small for Higgs masses around 120GeV but it quickly picks up
for higher Higgs masses especially because the one-loop amplitude develops a
leading Landau singularity and new thresholds open up. These effects can be
viewed as the production of a pair of top quarks which rescatter to give rise
to Higgs production through WW fusion. We study the leading Landau singularity
in detail. Since this singularity is not integrable when the one-loop amplitude
is squared, we regulate the cross section by taking into account the width of
the internal top and W particles. This requires that we extend the usual box
one-loop function to the case of imaginary masses. We show how this can be
implemented analytically in our case. We study in some detail the cross section
at the LHC as a function of the Higgs mass and show how some distributions can
be drastically affected compared to the tree-level result.Comment: 48 pages, 20 figures. Phys.Rev.D accepted version. Conclusions
unchanged, minor changes and references adde
High-field irreversible moment reorientation in the antiferromagnet FeTe
Magnetization measurements have been performed on single-crystalline
FeTe in pulsed magnetic fields up to 53 T
and temperatures from 4.2 to 65 K. At K, a non-reversible reorientation
of the antiferromagnetic moments is observed at T as the pulsed
field is on the rise. No anomaly is observed at during the fall of the
field and, as long as the temperature is unchanged, during both rises and falls
of additional field pulses. The transition at is reactivated if the
sample is warmed up above the N\'{e}el temperature K and cooled
down again. The magnetic field-temperature phase diagram of FeTe in
is also investigated. We present the temperature
dependence of , as well as that of the antiferromagnetic-to-paramagnetic
borderline in temperatures above 40 K.Comment: 5 pages, 4 figure
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Isolated OB Associations in Stripped HI Gas Clouds
HST ACS/HRC images in UV (F250W), V (F555W), and I (F814W) resolve three
isolated OB associations that lie up to 30 kpc from the stellar disk of the S0
galaxy NGC 1533. Previous narrow-band Halpha imaging and optical spectroscopy
showed these objects as unresolved intergalactic HII regions having Halpha
luminosities consistent with single early-type O stars. These young stars lie
in stripped HI gas with column densities ranging from 1.5 - 2.5 * 10^20 cm^-2
and velocity dispersions near 30 km s^-1. Using the HST broadband colors and
magnitudes along with previously-determined Halpha luminosities, we place
limits on the masses and ages of each association, considering the importance
of stochastic effects for faint (M_V >-8) stellar populations. The upper limits
to their stellar masses range from 600 M_sun to 7000 M_sun, and ages range from
2 - 6 Myrs. This analysis includes an updated calculation of the conversion
factor between the ionizing luminosity and the total number of main sequence O
stars contained within an HII region. The photometric properties and sizes of
the isolated associations and other objects in the HRC fields are consistent
with those of Galactic stellar associations, open clusters and/or single O and
B stars. We interpret the age-size sequence of associations and clustered field
objects as an indication that these isolated associations are most likely
rapidly dispersing. Furthermore, we consider the possibility that these
isolated associations represent the first generation of stars in the HI ring
surrounding NGC 1533. This work suggests star formation in the unique
environment of a galaxy's outermost gaseous regions proceeds similarly to that
within the Galactic disk and that star formation in tidal debris may be
responsible for building up a younger halo component.Comment: 21 pages, 9 figures, 6 tables; accepted for publication in Ap
Early-Childhood Growth Faltering, Post-Infancy Recovery and Educational Outcomes in Late Childhood: Evidence from Vietnam
We use longitudinal data on over 1,500 children born in 2001 in Vietnam to study the impact of early childhood stunting on height, lagging in schooling progression and cognitive outcomes in late childhood (age 8-10 years). Our preferred estimates utilize 2SLS estimators to control for the endogenous determination of early childhood stunting and also include control for child sex and birth order, motherâs height and BMI, household socioeconomic status, and community characteristics. These estimates indicate that deficits in height-for-age at age 12 months have negative impacts on height in late childhood but not on schooling and cognitive outcomes in late childhood. The children who were stunted or moderately stunted at age 12 months display significant catch-up growth, recovering half of their deficits in height-for-age by age 8 years. Socioeconomic status in infancy has negative effects on both stunting in infancy and poor subsequent educational outcomes in late childhood, which result in significant associations between stunting in infancy and some subsequent educational outcomes in late childhood â but not causal effects once there is control for the endogenous determination of early childhood height deficits
Infrastructure Model Development to Enhance Resilience against future changes using InfraWorks & GIS
The Smart City idea is becoming more popular because cities are getting too crowded. This study looks at how BIM and Geographical Information Systems (GIS) work together. The study focused on infrastructure and figuring out how long a building would last, as early stages of infrastructure development would help the public organization to better plan and design. The GIS mapping shows which areas are more likely to become cities or towns. The AEC industry stakeholders can benefit from mapping to achieve Sustainable Development Goals (SGDs). The AEC industry has also been constantly moving towards Building Information Modelling (BIM). In this study, the city of London was considered, and Land Cover predictions from 2000 to 2025 were made. The predicted Map of 2025 would help developers and planning authorities on decision making on housing development. Based on the current study, more research could be extended on how BIM and GIS could work together for urban development
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