3,346 research outputs found
A model-free sparse approximation approach to robust formal reaction kinetics
Accurate and transferable models of reaction kinetics are of key importance for chemical reactors on both laboratory and industrial scale. Usually, setting up such models requires a detailed mechanistic understanding of the reaction process and its interplay with the reactor setup. We present a data driven approach which analyzes the influence of process parameters on the reaction rate to identify locally approximated effective rate laws without prior knowledge and assumptions. The algorithm we propose determines relevant model terms from a polynomial ansatz employing well established statistical methods. For the optimization of the model parameters special emphasize is put on the robustness of the results by taking not only the quality of the fit but also the distribution of errors into account in a multi-objective optimization. We demonstrate the flexibility of this approach based on artificial kinetic data sets from microkinetic models. This way, we show that the kinetics of both the classical HBr reaction and a prototypical catalytic cycle are automatically reproduced. Further, combining our approach with experimental screening designs we illustrate how to efficiently explore kinetic regimes by using the example of the catalytic oxidation of CO
Demokratie auf dem Rückzug? Zur Konfrontation zwischen amerikanischem Präsidenten und Kongress über einen Truppenabzug aus dem Irak
Im US-Präsidentschaftswahlkampf 2008 ist der Irakkrieg eines der wichtigsten Themen. Die Amerikaner sind allmählich kriegsmüde und die Mehrheit befürwortet einen Truppenrückzug aus dem Irak. Das brachten bereits der Ausgang der Kongresswahlen im Jahr 2006 sowie regelmäßige Meinungsumfragen zum Ausdruck.
Es ist nun anzunehmen, dass in der ältesten Demokratie der Welt Volkes Wille direkten Einfluss auf die Politik haben müsste. Doch dies ist nur bedingt der Fall. Besonders Präsident George W. Bush hat wiederholt klargestellt, dass die Stimmung in der Bevölkerung für ihn in der Irakfrage nicht maßgebend sei. Für ihn zähle vielmehr, wie die Generäle vor Ort die aktuelle Sicherheitslage und die Fortschritte einschätzen. Dagegen versucht der seit Ende 2006 von Demokraten dominierte Kongress immer wieder, Rückzugspläne mit festen Fristen zu etablieren. Bislang ist sein Erfolg jedoch bescheiden.
Vor allem die fehlende Unterstützung der Republikaner im Kongress und die Blockadepolitik des Präsidenten waren dafür verantwortlich. Hinter der Konfrontation steht eine tiefergehende Auseinandersetzung über die Kompetenzverteilung zwischen Präsident und Kongress bei Kriegsentscheidungen, die in der US-Verfassung in einer Grauzone bleibt.
Stephanie Sohnius verknüpft vor diesem verfassungsrechtlichen Hintergrund die Aufarbeitung der aktuell wichtigsten USaußenpolitischen Debatte mit der Frage, ob sich die Demokratie in den USA in der Ära des „Krieges gegen den Terrorismus“ (weiterhin) auf dem Rückzug befindet
Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet
The electronic structure of the single molecule magnet system
M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray
photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission
spectroscopy, and density functional calculations. There is good agreement
between theoretical calculations and experimental data. The valence band mainly
consists of three bands between 2 eV and 30 eV. Both theory and experiments
show that the top of the valence band is dominated by the hybridization between
Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe
in the molecule is most likely in the 2+ charge state. Its neighboring atoms
(O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron
atom, giving a high spin state molecule with a total S=5 effective spin for the
case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy
Ten-Year Minimum Follow-up Study of First Metatarsophalangeal Joint Fusion in Young vs Old Patients
BACKGROUND
Painful degenerative joint disease (DJD) of the first metatarsophalangeal joint (MTP I), or hallux rigidus, mainly occurs in later stages of life. For end-stage hallux rigidus, MTP I arthrodesis is considered the gold standard. As young and active patients are affected considerably less frequently, it currently remains unclear, whether they benefit to the same extent. We hypothesized that MTP I arthrodesis in younger patients would lead to an inferior outcome with decreased rates of overall with lower rates of patient postoperative pain and function compared to an older cohort.
METHODS
All patients aged 60 years. Minimum follow-up was 10 years. Outcome measures were Tegner activity score (TAS), a "Virtual Tegner activity score" (VTAS), the visual analog scale (VAS), and the Foot Function index (FFI).
RESULTS
Sixty-one MTP I fusions (n = 28 young, n = 33 old) in 46 patients were included in our study at an average of 14 years after surgery. Younger patients experienced significantly more pain relief as reflected by changes in VAS and FFI Pain subscale scores. No difference in functional outcomes was found with change in the FFI function subscale or in the ability to have desired functional outcomes using the ratio of TAS to VTAS. Revision rate did not differ between the two groups apart from hardware removal, which was significantly more likely in the younger group.
CONCLUSION
In patients below the age of 50 years with end-stage DJD of the first metatarsal joint, MTP I arthrodesis not only yielded highly satisfactory postoperative results at least equal outcome compared to an older cohort of patients aged >60 years at an average 14 years' follow-up. Based on these findings, we consider first metatarsal joint fusion even for young patients is a valid option to treat end-stage hallux rigidus.
LEVEL OF EVIDENCE
Level III, a case-control study
Morphine-like action of enkephalin analog FK 33-824 on motility of the isolated rat colon.
ABSTRAC
Low energy measurement of the 7Be(p,gamma)8B cross section
We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm =
185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi).
Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^*
decay, respectively, were measured using a large acceptance spectrometer. The
zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a
weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is
deduced when combining this value with our previous results at higher energies.Comment: Accepted for publication in Phys. Rev. Let
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