503 research outputs found
Improving Atmospheric Angular Momentum Forecasts by Machine Learning
Earth angular momentum forecasts are naturally accompanied by forecast errors that typically grow with increasing forecast length. In contrast to this behavior, we have detected large quasi-periodic deviations between atmospheric angular momentum wind term forecasts and their subsequently available analysis. The respective errors are not random and have some hard to define yet clearly visible characteristics which may help to separate them from the true forecast information. These kinds of problems, which should be automated but involve some adaptation and decision-making in the process, are most suitable for machine learning methods. Consequently, we propose and apply a neural network to the task of removing the detected artificial forecast errors. We found that a cascading forward neural network model performed best in this problem. A total error reduction with respect to the unaltered forecasts amounts to about 30% integrated over a 6-days forecast period. Integrated over the initial 3-days forecast period, in which the largest artificial errors are present, the improvements amount to about 50%. After the application of the neural network, the remaining error distribution shows the expected growth with forecast length. However, a 24-hourly modulation and an initial baseline error of 2 Ă 10â8 became evident that were hidden before under the larger forecast error
Purification, characterisation and crystallisation of photosystem II from Thermosynechococcus elongatus cultivated in a new type of photobioreactor
AbstractThe thermophilic cyanobacterium Thermosynechococcus elongatus was cultivated under controlled growth conditions using a new type of photobioreactor, allowing us to optimise growth conditions and the biomass yield. A fast large-scale purification method for monomeric and dimeric photosystem II (PSII) solubilized from thylakoid membranes of this cyanobacterium was developed using fast protein liquid chromatography (FPLC). The obtained PSII core complexes (PSIIcc) were analysed for their pigment stoichiometry, photochemical and oxygen evolution activities, as well as lipid and detergent composition. Thirty-six chlorophyll a (Chla), 2 pheophytin a (Pheoa), 9± 1 ÎČ-carotene (Car), 2.9±0.8 plastoquinone 9 (PQ9) and 3.8±0.5 Mn were found per active centre. For the monomeric and dimeric PSIIcc, 18 and 20 lipid as well as 145 and 220 detergent molecules were found in the detergent shell, respectively. The monomeric and dimeric complexes showed high oxygen evolution activity with 1/4 O2 released per 37â38 Chla and flash in the best cases. Crystals were obtained from dimeric PSIIcc by a micro-batch method. They diffract synchrotron X-rays to a maximum resolution of 2.9-Ă
, resulting in complete data sets of 3.2 Ă
resolution
Estimating ocean tide model uncertainties for electromagnetic inversion studies
Over a decade ago the semidiurnal lunar M2 ocean tide was identified in CHAMP
satellite magnetometer data. Since then and especially since the launch of
the satellite mission Swarm, electromagnetic tidal observations from
satellites are increasingly used to infer electric properties of the upper
mantle. In most of these inversions, ocean tidal models are used to generate
oceanic tidal electromagnetic signals via electromagnetic induction. The
modeled signals are subsequently compared to the satellite observations.
During the inversion, since the tidal models are considered error free,
discrepancies between forward models and observations are projected only onto
the induction part of the modeling, e.g., Earth's conductivity distribution.
Our study analyzes uncertainties in oceanic tidal models from an
electromagnetic point of view. Velocities from hydrodynamic and assimilative
tidal models are converted into tidal electromagnetic signals and compared.
Respective uncertainties are estimated. The studies main goal is to provide
errors for electromagnetic inversion studies. At satellite height, the
differences between the hydrodynamic tidal models are found to reach up to
2 nT, i.e., over 100 % of the local M2 signal. Assimilative tidal models
show smaller differences of up to 0.1 nT, which in some locations still
corresponds to over 30 % of the M2 signal.</p
The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
Hypervelocity stars (HVS) travel with velocities so high, that they exceed
the escape velocity of the Galaxy. Several acceleration mechanisms have been
discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we
present a spectroscopic and kinematic analysis of US\,708. Travelling with a
velocity of , it is the fastest unbound star in our
Galaxy. In reconstructing its trajectory, the Galactic center becomes very
unlikely as an origin, which is hardly consistent with the most favored
ejection mechanism for the other HVS. Furthermore, we discovered US\,708 to be
a fast rotator. According to our binary evolution model it was spun-up by tidal
interaction in a close binary and is likely to be the ejected donor remnant of
a thermonuclear supernova.Comment: 16 pages report, 20 pages supplementary material
Double-helix Wilson loops: case of two angular momenta
Recently, Wilson loops with the shape of a double helix have played an
important role in studying large spin operators in gauge theories. They
correspond to a quark and an anti-quark moving in circles on an S3 (and
therefore each of them describes a helix in RxS3). In this paper we consider
the case where the particles have two angular momenta on the S3. The string
solution corresponding to such Wilson loop can be found using the relation to
the Neumann-Rosochatius system allowing the computation of the energy and
angular momenta of the configuration. The particular case of only one angular
momentum is also considered. It can be thought as an analytic continuation of
the rotating strings which are dual to operators in the SL(2) sector of N=4
SYM.Comment: 30 pages, 2 figures, LaTeX. v2: Small corrections, reference adde
Electromagnetic characteristics of ENSO
The motion of electrically conducting sea water through Earth's magnetic
field induces secondary electromagnetic fields. Due to its periodicity, the
oceanic tidally induced magnetic field is easily distinguishable in magnetic
field measurements and therefore detectable. These tidally induced signatures
in the electromagnetic fields are also sensitive to changes in oceanic
temperature and salinity distributions. We investigate the impact of oceanic
heat and salinity changes related to the El NiñoâSouthern Oscillation (ENSO)
on oceanic tidally induced magnetic fields. Synthetic hydrographic
data containing characteristic ENSO dynamics have been derived from a coupled
oceanâatmosphere simulation covering a period of 50Â years. The corresponding
tidally induced magnetic signals have been calculated with the 3-D induction
solver x3dg. By means of the Oceanic Niño Index (ONI), based on sea surface
temperature anomalies, and a corresponding Magnetic Niño Index (MaNI),
based on anomalies in the oceanic tidally induced magnetic field at sea
level, we demonstrate that evidence of developing ENSO events can be found in
the oceanic magnetic fields statistically 4 months earlier than in sea
surface temperatures. The analysis of the spatio-temporal progression of the
oceanic magnetic field anomalies offers a deeper understanding on the
underlying oceanic processes and is used to test and validate the initial
findings
Use of controlled low dose gamma irradiation to sterilize allograft tendons for ACL reconstruction: biomechanical and clinical perspective
As reviewed here, numerous biomechanical and clinical studies support the use of controlled, low temperature irradiation of allograft tendons, to provide both excellent clinical results and medical-device grade sterile allografts with minimal risk of disease transmission
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
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