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81.
82.
We generalize an integral representation for the ruin probability in a Crámer-Lundberg risk model with shifted (or also called US-)Pareto claim sizes, obtained by Ramsay (2003), to classical Pareto(a) claim size distributions with arbitrary real values a>1 and derive its asymptotic expansion. Furthermore an integral representation for the tail of compound sums of Pareto-distributed claims is obtained and numerical illustrations of its performance in comparison to other aggregate claim approximations are provided. 相似文献
83.
84.
Dominik Schröder Kai Banke Sebastian A. Kaiser Burak Atakan 《Proceedings of the Combustion Institute》2021,38(4):5567-5574
Fuel-rich combustion of methane in a homogeneous-charge compression-ignition (HCCI) engine can be used as a polygeneration process producing work, heat, and useful chemicals like syngas. Due to the inertness of methane, additives such as dimethyl ether (DME) are needed to achieve ignition at moderate inlet temperatures and to control combustion phasing. Because significant concentrations of DME are then needed, a considerable part of the fuel energy comes from DME. An alternative ignition promotor known from fuel-lean HCCI is ozone (O3). Here, a combined experimental and modelling study on the ignition of fuel-rich partial oxidation of methane/air mixtures at Φ = 1.9 with ozone and DME as additives in an HCCI engine is conducted. Experimental results show that ozone is a suitable additive for fuel-rich HCCI, with only 75 ppm ozone reducing the fuel-fraction of DME needed from 11.0% to 5.3%. Since ozone does not survive until the end of the compression stroke, the reaction paths are analyzed in a single-zone model. The simulation shows that different ignition precursors or buffer molecules are formed, depending on the additives. If only DME is added, hydrogen peroxide (H2O2) and formaldehyde (CH2O) are the most important intermediates, leading to OH formation and ignition around top dead center (TDC). With ozone addition, methyl hydroperoxide (CH3OOH) becomes very important earlier in the compression stroke under these fuel-rich conditions. It is then later converted to CH2O and H2O2. Thus, ozone is a very effective additive not only for fuel-lean, but also for fuel-rich combustion. However, the mechanism differs between both regimes. Because less of the expensive additives are needed, ozone could help improving the economics of a polygeneration process with fuel-rich operated HCCI engines. 相似文献
85.
Laura Senft Jamonica L. Moore Alicja Franke Katherine R. Fisher Andreas Scheitler Achim Zahl Ralph Puchta Dominik Fehn Sidney Ison Safaa Sader Ivana Ivanovi-Burmazovi Christian R. Goldsmith 《Chemical science》2021,12(31):10483
Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H2O2, [Mn(H2qp1)(MeCN)]2+ and [Mn(H4qp2)Br2], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]+ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O2˙− to O2 and H2O2, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O2˙− in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O2˙− to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O2˙− oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (kcat ∼ 108 M−1 s−1 at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics.Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species. 相似文献
86.
The mechanism of the decomposition of acryloylcarbamates 7a–b yielding highly reactive isocyanates 3a–b was proposed based on NMR measurements and quantum chemical calculations. A good agreement between the experimental kinetic data and DFT calculations allowed us to demonstrate that the stability of 7a–d depends on the presence of methyl in the acryloyl moiety and the position of the nitro group in the nitrophenolic part of the molecule. Furthermore, the reactivity of 7a–d with weakly nucleophilic and sterically hindered 2,4,6‐tri‐tert‐butylaniline was explored by 1H NMR demonstrating the usefulness of reagents 7a–d offering access to a variety of 1‐N‐substituted uracils and thymines with potentially interesting biological properties. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
87.
Sheetal Saxena Alexander Summa Dominik Elsässer Michael Rüger Karl Mannheim 《The European Physical Journal C - Particles and Fields》2011,71(11):1815
As the largest mass concentrations in the local Universe, nearby clusters of galaxies and their central galaxies are prime
targets in searching for indirect signatures of dark matter annihilation (DMA). We seek to constrain the dark matter annihilation
emission component from multi-frequency observations of the central galaxy of the Virgo cluster. The annihilation emission
component is modeled by the prompt and inverse-Compton gamma rays from the hadronization of annihilation products from generic
weakly interacting dark matter particles. This component is fitted to the excess of the observed data above the spectral energy
distribution (SED) of the jet in M87, described with a best-fit synchrotron-self-Compton (SSC) spectrum. While this result
is not sufficiently significant to claim a detection, we emphasize that a dark matter “double hump signature” can be used
to unambiguously discriminate the dark matter emission component from the variable jet-related emission of M87 in future,
more extended observation campaigns. 相似文献
88.
89.
Alois Pfenniger Andreas Stahel Volker M. Koch Dominik Obrist Rolf Vogel 《Applied Mathematical Modelling》2014
Engineers are confronted with the energy demand of active medical implants in patients with increasing life expectancy. Scavenging energy from the patient’s body is envisioned as an alternative to conventional power sources. Joining in this effort towards human-powered implants, we propose an innovative concept that combines the deformation of an artery resulting from the arterial pressure pulse with a transduction mechanism based on magneto-hydrodynamics. To overcome certain limitations of a preliminary analytical study on this topic, we demonstrate here a more accurate model of our generator by implementing a three-dimensional multiphysics finite element method (FEM) simulation combining solid mechanics, fluid mechanics, electric and magnetic fields as well as the corresponding couplings. This simulation is used to optimize the generator with respect to several design parameters. A first validation is obtained by comparing the results of the FEM simulation with those of the analytical approach adopted in our previous study. With an expected overall conversion efficiency of 20% and an average output power of 30 μW, our generator outperforms previous devices based on arterial wall deformation by more than two orders of magnitude. Most importantly, our generator provides sufficient power to supply a cardiac pacemaker. 相似文献
90.
Dominik Schindele Robert Prabel 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(2):105-129
This contribution presents two real-time capable nonlinear model-predictive control (NMPC) approaches for an electro-pneumatic clutch for heavy trucks: a centralized control approach and a cascaded one. A clutch is necessary at start-up or during gear shifts to connect or disconnect the combustion engine and the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque typically transmitted through the drive train. The force characteristic of the clutch, however, is subject to hysteresis, which is described by a generalized Bouc–Wen model and used for a feedforward hysteresis compensation in the control algorithm. The proposed NMPC-algorithm involves (i) a minimization of the difference between the desired and predicted state vector at the end of the prediction horizon and (ii) flatness-based techniques to compute desired trajectories for the complete state vector as well as the control input. The optimal control is given by an additional, minimum-norm control input that minimizes the difference between the predicted state vector and the desired one at the end of the prediction horizon. Thereby, the computation effort of the NMPC approaches can be kept relatively small, and a real-time evaluation becomes possible. A reduced-order observer estimates an effective pressure in the clutch that also accounts for an uncertain disturbance force. Thereby, a disturbance compensation and a high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the two proposed control structures is emphasized by experimental results from a dedicated test rig. 相似文献