1,864 research outputs found
Galactic Center Radio Constraints on Gamma-Ray Lines from Dark Matter Annihilation
Recent evidence for one or more gamma-ray lines at ~ 130 GeV in the Fermi-LAT
data from the Galactic Center has been interpreted as a hint for dark matter
annihilation to Z{\gamma} or H{\gamma} with an annihilation cross section,
~ 10^{-27} cm^3 s^{-1} . We test this hypothesis by comparing
synchrotron fluxes due to the electrons and positrons from the decay of the Z
or the H boson only in the Galactic Center against radio data from the same
region in the Galactic Center. We find that the radio data from single dish
telescopes marginally constrain this interpretation of the claimed gamma lines
for a contracted NFW profile. Already-operational radio telescopes such as LWA,
VLA-Low and LOFAR, and future radio telescopes like SKA, which are sensitive to
annihilation cross sections as small as 10^{-28} cm^3 s^{-1}, can confirm or
rule out this scenario very soon. We discuss the assumptions on the dark matter
profile, magnetic fields, and background radiation density profiles, and show
that the constraints are relatively robust for any reasonable assumptions.
Independent of the above said recent developments, we emphasize that our radio
constraints apply to all models where dark matter annihilates to Z{\gamma} or
H{\gamma}.Comment: v3: 18 pages, 7 figures. Minor changes. Published in Phys. Rev.
Using Absorption Imaging to Study Ion Dynamics in an Ultracold Neutral Plasma
We report optical absorption imaging of ultracold neutral plasmas.Images are
used to measure the ion absorption spectrum, which is Doppler-broadened.
Through the spectral width, we monitor ion equilibration in the first 250ns
after plasma formation. The equilibration leaves ions on the border between the
weakly coupled gaseous and strongly coupled liquid states. On a longer
timescale of microseconds, we observe radial acceleration of ions resulting
from pressure exerted by the trapped electron gas.Comment: 4 pages, 4 figure
Species distribution mapping and sustainability measures for a fungus economy in the Indian Himalaya
This presentation was given as part of the GIS Day@KU symposium on November 16, 2016. For more information about GIS Day@KU activities, please see http://gis.ku.edu/gisday/2016/.A entomopathogenic fungus, a fungus that kills its host caterpillar to proliferate. This fungus cures a plethora of ailments. It is one of the most expensive natural resources of the world and a resource that emancipated many from poverty in the remote mountains in the Tibetan plateau and the adjoining high altitude areas of Central and Eastern Himalaya. Geographically, a fine resolution information is lacking for majority of its distribution area. We explored a small region Askot landscape in the state Uttarakhand in Western Himalaya in India. The quest culminated in an extensive questionnaire survey with the villagers and harvesters. A current distribution map based on survey and a predicted suitable zone map using MaXent was produced. The concept is based on distributional ecology of a species which cross sections into concepts of species distribution model and ecological niche modelling. The inputs included both abiotic and biotic factos, albiet complexity. After repeated calibration and manual evaluation analysis, we chose elevation, aspect, slope and 12 PCA inputs of 68 MODIS 13Q1 NDVI layers (2012-2013) as the input data. Presence only data distributed as 10 random replicate pairs is used for training data and evalutation. Occurrence data is error free as it is a primary source data. Model evaluation returned a AUC ratio > 1 values for each, indicating that Maxent curve was significantly elevated above the bull expectations. The process of generating a suitability map convinced us of a sustainable harvest approach for safeguarding direct benefit to people's livelihood and indirectly the local environment.Platinum Sponsors: KU Department of Geography and Atmospheric Science. Gold Sponsors: Enertech, KU Environmental Studies Program, KU Libraries. Silver Sponsors: Douglas County, Kansas, KansasView, State of Kansas Data Access & Support Center (DASC) and the KU Center for Global and International Studies
Extreme Warm Absorber variability in the Seyfert Galaxy Mrk 704
In about half of Seyfert galaxies, the X-ray emission is absorbed by an
optically thin, ionized medium, the so-called "Warm Absorber", whose origin and
location is still a matter of debate. The aims of this paper is to put more
constraints on the warm absorber by studying its variability. We analyzed the
X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three
years apart, by XMM-Newton. The spectra were well fitted with a two zones
absorber, possibly covering only partially the source. The parameters of the
absorbing matter - column density, ionization state, covering factor - changed
significantly between the two observations. Possible explanations for the more
ionized absorber are a torus wind (the source is a polar scattering one) or, in
the partial covering scenario, an accretion disk wind. The less ionized
absorber may be composed of orbiting clouds in the surroundings of the nucleus,
similarly to what already found in other sources, most notably NGC 1365.Comment: 10 pages. Accepted for publication in Astronomy & Astrophysic
Absorption Imaging and Spectroscopy of Ultracold Neutral Plasmas
Absorption imaging and spectroscopy can probe the dynamics of an ultracold
neutral plasma during the first few microseconds after its creation.
Quantitative analysis of the data, however, is complicated by the inhomogeneous
density distribution, expansion of the plasma, and possible lack of global
thermal equilibrium for the ions. In this article we describe methods for
addressing these issues. Using simple assumptions about the underlying
temperature distribution and ion motion, the Doppler-broadened absorption
spectrum obtained from plasma images can be related to the average temperature
in the plasma.Comment: 14 pages, 8 figure
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Solubilization and biodegradation of hydrophobic organic compounds in soil/aqueous systems with nonionic surfactants
Nonionic surfactants may strongly interact with hydrophobic organic compounds (HOCs), soil, and microorganisms in soil/aqueous systems. These interactions affect the potential for surfactant-facilitated HOC transport in soil and groundwater systems, and the feasibility of engineered surfactant cleanup of contaminated sites (McCarthy and Wober, 1991). At sufficiently high bulk liquid concentrations at 25 C, most nonionic surfactants form regular micelles in single-phase solutions, whereas certain surfactants, such as C{sub 12}E{sub 4}, may form bilayer lamellae or other types of aggregates in more complex two-phase solutions. The critical concentrations for the onset of micelle and aggregate formation are termed the critical micelle concentration (CMC) and the critical aggregation concentration (CAC), respectively. Important changes occur in surfactant sorption, surfactant solubilization of HOCs, and microbial mineralization of HOCs in the presence of nonionic surfactants at or near these critical surfactant concentrations
Ultracold Neutral Plasmas
Ultracold neutral plasmas are formed by photoionizing laser-cooled atoms near
the ionization threshold. Through the application of atomic physics techniques
and diagnostics, these experiments stretch the boundaries of traditional
neutral plasma physics. The electron temperature in these plasmas ranges from
1-1000 K and the ion temperature is around 1 K. The density can approach
cm. Fundamental interest stems from the possibility of
creating strongly-coupled plasmas, but recombination, collective modes, and
thermalization in these systems have also been studied. Optical absorption
images of a strontium plasma, using the Sr
transition at 422 nm, depict the density profile of the plasma, and probe
kinetics on a 50 ns time-scale. The Doppler-broadened ion absorption spectrum
measures the ion velocity distribution, which gives an accurate measure of the
ion dynamics in the first microsecond after photoionization.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Magnetic trapping of metastable atomic strontium
We report the magnetic trapping of metastable atomic strontium. Atoms
are cooled in a magneto-optical trap (MOT) operating on the dipole allowed
transition at 461 nm. Decay via
continuously loads a magnetic trap formed by the quadrupole magnetic field of
the MOT. Over atoms at a density of cm and
temperature of 1 mK are trapped. The atom temperature is significantly lower
than what would be expected from the kinetic and potential energy of atoms as
they are transferred from the MOT. This suggests that thermalization and
evaporative cooling are occurring in the magnetic trap.Comment: This paper has been accepted by PR
Solution of the relativistic Dirac-Hulthen problem
The one-particle three-dimensional Dirac equation with spherical symmetry is
solved for the Hulthen potential. The s-wave relativistic energy spectrum and
two-component spinor wavefunctions are obtained analytically. Conforming to the
standard feature of the relativistic problem, the solution space splits into
two distinct subspaces depending on the sign of a fundamental parameter in the
problem. Unique and interesting properties of the energy spectrum are pointed
out and illustrated graphically for several values of the physical parameters.
The square integrable two-component wavefunctions are written in terms of the
Jacobi polynomials. The nonrelativistic limit reproduces the well-known
nonrelativistic energy spectrum and results in Schrodinger equation with a
"generalized" three-parameter Hulthen potential, which is the sum of the
original Hulthen potential and its square.Comment: 13 pages, 3 color figure
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