885 research outputs found
Support schemes for renewable electricity in the EU
This paper discusses the level and design of support schemes used to promote renewable electricity in Europe. A theoretical model is presented to determine optimal renewable energy policies. Policies that solely aim to address environmental externalities and energy security risks are unlikely to make renewable power technologies competitive. Learning effects and spillovers are necessary to justify the need for support schemes. The analysis suggests that feed-in premiums guaranteed in addition to the electricity market price should be preferred over feed-in tariffs, which provide the eligible power producer with a guaranteed price. The premiums should be time limited and frequently reviewed. Once the technology becomes competitive, tradable green certificates would be a more suitable support instrument. As regards wind energy, the available estimates of externalities suggest that levels are probably too high in many Member States. In addition, the current promotion of photovoltaics could possibly be more cost-efficient if it targeted technology development more directly.european union, eu, setzer, wolff, van den Noord, euro area, money, heterogeneity, money holdings
Proposal for a two-channel quantum dot setup: Prediction for the capacitance lineshape
We have made a detailed proposal for a two-channel quantum dot setup. The
energy scales in the problem are such that we are able to make connection with
the two-channel Anderson model, which, in spite of being well-known in the
context of heavy-Fermion systems remained theoretically elusive until recently
and lacked a mesoscopic realization. Verification of our precise and robust
predictions for the differential capacitance lineshape of the dot will provide
an experimental signature of the two-channel behavior.Comment: Proceedings for SCES conference (2005
Renormalization Group Approach to Spectral Properties of the Two-Channel Anderson Impurity Model
The impurity Green function and dynamical susceptibilties for the two-channel
Anderson impurity model are calculated. An exact expression for the self-energy
of the impurity Green function is derived. The imaginary part of the
self-energy scales as \sqrt{|\w/T_K|} for serving as a hallmark for
non-Fermi behavior. The many-body resonance is pinned to a universal value
at \w=0. Its shape becomes increasingly more symmetric for
the Kondo-regimes of the model. The dynamical susceptibilities are governed by
two energy scales and and approach a constant value for \w\to 0,
whereas relation \chi''(\w)\propto \w holds for the single channel model.Comment: 4 pages, 4 figure, revte
Persistent currents through a quantum impurity: Protection through integrability
We consider an integrable model of a one-dimensional mesoscopic ring with the
conduction electrons coupled by a spin exchange to a magnetic impurity. A
symmetry analysis based on a Bethe Ansatz solution of the model reveals that
the current is insensitive to the presence of the impurity. We argue that this
is true for any integrable impurity-electron interaction, independent of choice
of physical parameters or couplings. We propose a simple physical picture of
how the persistent current gets protected by integrability.Comment: 5 pages, minor update
High arsenic (As) concentrations in the shallow groundwaters of southern Louisiana: Evidence of microbial controls on As mobilization from sediments
Citation: Yang, N., Shen, Z., Datta, S., & Johannesson, K. H. (2016). High arsenic (As) concentrations in the shallow groundwaters of southern Louisiana: Evidence of microbial controls on As mobilization from sediments. Journal of Hydrology: Regional Studies, 5, 100-113. doi:10.1016/j.ejrh.2015.11.023Study region: The Mississippi Delta in southern Louisiana, United States. Study focus: The probable role that microbial respiration plays in As release from the shallow aquifer sediments. New hydrological insights for the region: Shallow groundwaters in southern Louisiana have been reported to contain elevated As concentrations, whereas mechanisms responsible for As release from sediments have rarely been studied in this region. Microbial respiration is generally considered the main mechanism controlling As release in reducing anoxic aquifers such as the shallow aquifers in southern Louisiana and those of the Bengal basin. This study investigates the role microbial respiration plays in As release from shallow aquifer sediments in southern Louisiana through sediment incubation experiments and porewater analysis. Arsenic concentrations were the lowest in the sterilized control experiments, slightly higher in the un-amended experiments, and the highest in the experiments amended with acetate, and especially those amended with both acetate and AQDS (9,10-anthraquinone-2,6-disulfonic acid). Although Fe and Mn generally decreased at the beginning of all the experiments, they did follow a similar trend to As after the decrease. Porewater analysis showed that As and Fe concentrations were generally positively correlated and were higher in the coarse-grained sediments than in the fine-grained sediments. Results of the investigation are consistent with microbial respiration playing a key role in As release from the shallow aquifers sediments in southern Louisiana. © 2015 The Authors
Energy Injection in GRB Afterglow Models
We extend the standard fireball model, widely used to interpret gamma-ray
burst (GRB) afterglow light curves, to include energy injections, and apply the
model to the afterglow light curves of GRB 990510, GRB 000301C and GRB 010222.
We show that discrete energy injections can cause temporal variations in the
optical light curves and present fits to the light curves of GRB 000301C as an
example. A continuous injection may be required to interpret other bursts such
as GRB 010222. The extended model accounts reasonably well for the observations
in all bands ranging from X-rays to radio wavelengths. In some cases, the radio
light curves indicate that additional model ingredients may be needed.Comment: Accepted for publication in the Astrophysical Journa
The Fine-Structure of the Net-Circular Polarization in a Sunspot Penumbra
We present novel evidence for a fine structure observed in the net-circular
polarization (NCP) of a sunspot penumbra based on spectropolarimetric
measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first
time we detect a filamentary organized fine structure of the NCP on spatial
scales that are similar to the inhomogeneities found in the penumbral flow
field. We also observe an additional property of the visible NCP, a
zero-crossing of the NCP in the outer parts of the center-side penumbra, which
has not been recognized before. In order to interprete the observations we
solve the radiative transfer equations for polarized light in a model penumbra
with embedded magnetic flux tubes. We demonstrate that the observed
zero-crossing of the NCP can be explained by an increased magnetic field
strength inside magnetic flux tubes in the outer penumbra combined with a
decreased magnetic field strength in the background field. Our results strongly
support the concept of the uncombed penumbra
Deciphering the local Interstellar spectra of primary cosmic ray species with HelMod
Local interstellar spectra (LIS) of primary cosmic ray (CR) nuclei, such as
helium, oxygen, and mostly primary carbon are derived for the rigidity range
from 10 MV to ~200 TV using the most recent experimental results combined with
the state-of-the-art models for CR propagation in the Galaxy and in the
heliosphere. Two propagation packages, GALPROP and HelMod, are combined into a
single framework that is used to reproduce direct measurements of CR species at
different modulation levels, and at both polarities of the solar magnetic
field. The developed iterative maximum-likelihood method uses GALPROP-predicted
LIS as input to HelMod, which provides the modulated spectra for specific time
periods of the selected experiments for model-data comparison. The interstellar
and heliospheric propagation parameters derived in this study are consistent
with our prior analyses using the same methodology for propagation of CR
protons, helium, antiprotons, and electrons. The resulting LIS accommodate a
variety of measurements made in the local interstellar space (Voyager 1) and
deep inside the heliosphere at low (ACE/CRIS, HEAO-3) and high energies
(PAMELA, AMS-02).Comment: 13 pages, 13 figures, 6 tables, ApJ in press. arXiv admin note: text
overlap with arXiv:1704.0633
HelMod in the works: from direct observations to the local interstellar spectrum of cosmic-ray electrons
The local interstellar spectrum (LIS) of cosmic-ray (CR) electrons for the
energy range 1 MeV to 1 TeV is derived using the most recent experimental
results combined with the state-of-the-art models for CR propagation in the
Galaxy and in the heliosphere. Two propagation packages, GALPROP and HelMod,
are combined to provide a single framework that is run to reproduce direct
measurements of CR species at different modulation levels, and at both
polarities of the solar magnetic field. An iterative maximum-likelihood method
is developed that uses GALPROP-predicted LIS as input to HelMod, which provides
the modulated spectra for specific time periods of the selected experiments for
model-data comparison. The optimized HelMod parameters are then used to adjust
GALPROP parameters to predict a refined LIS with the procedure repeated subject
to a convergence criterion. The parameter optimization uses an extensive data
set of proton spectra from 1997-2015. The proposed CR electron LIS accommodates
both the low-energy interstellar spectra measured by Voyager 1 as well as the
high-energy observations by PAMELA and AMS-02 that are made deep in the
heliosphere; it also accounts for Ulysses counting rate features measured out
of the ecliptic plane. The interstellar and heliospheric propagation parameters
derived in this study agree well with our earlier results for CR protons,
helium nuclei, and anti-protons propagation and LIS obtained in the same
framework.Comment: 11 pages, 14 figures, 4 tables; ApJ, in pres
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