40 research outputs found
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Assimilation of 3D radar reflectivities with an ensemble Kalman filter on the convective scale
An ensemble data assimilation system for 3D radar reflectivity data is introduced for the convection-permitting numerical weather prediction model of the COnsortium for Small-scale MOdelling (COSMO) based on the Kilometre-scale ENsemble Data Assimilation system (KENDA), developed by Deutscher Wetterdienst and its partners. KENDA provides a state-of-the-art ensemble data assimilation system on the convective scale for operational data assimilation and forecasting based on the Local Ensemble Transform Kalman Filter (LETKF). In this study, the Efficient Modular VOlume RADar Operator is applied for the assimilation of radar reflectivity data to improve short-term predictions of precipitation. Both deterministic and ensemble forecasts have been carried out. A case-study shows that the assimilation of 3D radar reflectivity data clearly improves precipitation location in the analysis and significantly improves forecasts for lead times up to 4 h, as quantified by the Brier Score and the Continuous Ranked Probability Score. The influence of different update rates on the noise in terms of surface pressure tendencies and on the forecast quality in general is investigated. The results suggest that, while high update rates produce better analyses, forecasts with lead times of above 1 h benefit from less frequent updates. For a period of seven consecutive days, assimilation of radar reflectivity based on the LETKF is compared to that of DWD's current operational radar assimilation scheme based on latent heat nudging (LHN). It is found that the LETKF competes with LHN, although it is still in an experimental phase
Collective Excitations of Holographic Quantum Liquids in a Magnetic Field
We use holography to study N=4 supersymmetric SU(Nc) Yang-Mills theory in the
large-Nc and large-coupling limits coupled to a number Nf << Nc of
(n+1)-dimensional massless supersymmetric hypermultiplets in the Nc
representation of SU(Nc), with n=2,3. We introduce a temperature T, a baryon
number chemical potential mu, and a baryon number magnetic field B, and work in
a regime with mu >> T,\sqrt{B}. We study the collective excitations of these
holographic quantum liquids by computing the poles in the retarded Green's
function of the baryon number charge density operator and the associated peaks
in the spectral function. We focus on the evolution of the collective
excitations as we increase the frequency relative to T, i.e. the
hydrodynamic/collisionless crossover. We find that for all B, at low
frequencies the tallest peak in the spectral function is associated with
hydrodynamic charge diffusion. At high frequencies the tallest peak is
associated with a sound mode similar to the zero sound mode in the
collisionless regime of a Landau Fermi liquid. The sound mode has a gap
proportional to B, and as a result for intermediate frequencies and for B
sufficiently large compared to T the spectral function is strongly suppressed.
We find that the hydrodynamic/collisionless crossover occurs at a frequency
that is approximately B-independent.Comment: 45 pages, 8 png and 47 pdf images in 22 figure
On Uniqueness of supersymmetric Black holes in AdS(5)
We study the possibility of having Black hole of spherical and ring horizon
topology with five independent charges in the -model of 5D gauge
supergravity. To study these possibilities we consider not only the known
result obtained by local supersymmetry analysis but include the input coming
from non-local properties of the solutions, like the attractor mechanism, the
entropy function of Sen, the Euclidean formulation and general properties of
the uplift to ten dimension. For the spherical case, we found that there is no
room for more general Black holes than the ones already describe in
hep-th/0601156. On the other hand, if a solution of ring horizon topology
exists, we conclude that it must be labeled by three independent parameters
only, since it has to satisfy two independent constraints that we explicitly
find in terms of its chemical potentials. At the end of the article, based on
all the local and non-local information, we put forward a conjecture on the
constraints that characterize general Black holes dual to SYM.Comment: 16 pages, typos corrected and references adde
Holographic Roberge-Weiss Transitions II: Defect Theories and the Sakai-Sugimoto Model
We extend the work of Aarts et al., including an imaginary chemical potential
for quark number into the Sakai-Sugimoto model and codimension k defect
theories. The phase diagram of these models are a function of three parameters,
the temperature, chemical potential and the asymptotic separation of the
flavour branes, related to a mass for the quarks in the boundary theories. We
compute the phase diagrams and the pressure due to the flavours of the theories
as a function of these parameters and show that there are Roberge-Weiss
transitions in the high temperature phases, chiral symmetry restored for the
Sakai-Sugimoto model and deconfined for the defect models, while at low
temperatures there are no Roberge-Weiss transitions. In all the models we
consider the transitions between low and high temperature phases are first
order, hence the points where they meet the Roberge-Weiss lines are triple
points. The pressure for the defect theories scales in the way we expect from
dimensional analysis while the Sakai-Sugimoto model exhibits unusual scaling.
We show that the models we consider are analytic in \mu^2 when \mu^2 is small.Comment: 39 pages, 12 figures. references added, Sakai-Sugimoto section
revised, version to appear in JHE
Virtual reality for improved human-computer interaction in robotics and medicine
This paper describes a new technology for human-computer interaction, known as Virtual Reality. The paper illustrates the potential of this new technology with the summary of recent development work at the Fraunhofer-Institute for Manufacturing Engineering and Automation, which has made possible the use of Virtual Reality for the off-line programming and remote operation of industrial robots. The paper goes on to indicate how experience gained in engineering applications can provide significant benefits in medicine
Model-based flexibility assessment of a residential heat pump pool
This paper presents and demonstrates a methodology to explore the flexibility of a heat pump pool. Three points are in the focus of this work: First the procedure to model a pool of residential heat pump systems. Second the study of the response of a large number of heat pumps when the Smart-Grid-Ready interface is used for direct load control. Third a general assessment of flexibility of a pool of heat pump systems. The presented pool model accounts for the diversity in space heating and domestic hot water demands, the types of heat source and heat distribution systems used and system sizing procedures. The model is validated using field test data. Flexibility is identified by sending trigger signals to a pool of 284 SG-Ready heat pumps and evaluating the response. Flexibility is characterized by maximum power, shiftable energy and regeneration time. Results show that flexibility is highly dependent on the ambient temperature and the use of an electric back-up heater. It is found that using SG-Ready-like signals offers significantly higher flexibility than just switching off heat pumps, as it is mostly done today