Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring

The Optical Frequency Comb as a One-Way Quantum Computer

In the one-way model of quantum computing, quantum algorithms are implemented using only measurements on an entangled initial state. Much of the hard work is done up-front when creating this universal resource, known as a cluster state, on which the measurements are made. Here we detail a new proposal for a scalable method of creating cluster states using only a single multimode optical parametric oscillator (OPO). The method generates a continuous-variable cluster state that is universal for quantum computation and encoded in the quadratures of the optical frequency comb of the OPO. This work expands on the presentation in Phys. Rev. Lett. 101, 130501 (2008).Comment: 20 pages, 8 figures. v2 corrects minor error in published versio

Heisenberg-limited qubit readout with two-mode squeezed light

We show how to use two-mode squeezed light to exponentially enhance cavity-based dispersive qubit measurement. Our scheme enables true Heisenberg-limited scaling of the measurement, and crucially, is not restricted to small dispersive couplings or unrealistically long measurement times. It involves coupling a qubit dispersively to two cavities, and making use of a symmetry in the dynamics of joint cavity quadratures (a so-called quantum-mechanics-free subsystem). We discuss the basic scaling of the scheme and its robustness against imperfections, as well as a realistic implementation in circuit quantum electrodynamics.Comment: 5 pages, 4 figures, Supplemental Materia

Sequentially mixing modes in an election survey

In this paper, we analyze to what extent a sequential mixed mode survey, consisting of push-to-web, telephone and mail-paper modes, is able to improve representativeness in terms of socio-demographic variables and reduce bias in terms of voting behavior compared to a single mode survey. In addition, we study whether changes in mode lead to measurement error issues by focusing on income. We find that adding the telephone mode improves sample representation in terms of socio-demographic variables. Meanwhile, adding the paper mode does not show further improvements in this respect. However, adding the telephone, and in particular the paper mode, turn out to reduce bias in voting behavior when compared to official figures. As for measuring income, the web and the telephone mode perform similarly well. Finally, we find little evidence of measurement differences of income when the same respondents are interviewed first by web or telephone and subsequently by paper questionnaire

Repairing Ontologies via Axiom Weakening.

Ontology engineering is a hard and error-prone task, in which small changes may lead to errors, or even produce an inconsistent ontology. As ontologies grow in size, the need for automated methods for repairing inconsistencies while preserving as much of the original knowledge as possible increases. Most previous approaches to this task are based on removing a few axioms from the ontology to regain consistency. We propose a new method based on weakening these axioms to make them less restrictive, employing the use of refinement operators. We introduce the theoretical framework for weakening DL ontologies, propose algorithms to repair ontologies based on the framework, and provide an analysis of the computational complexity. Through an empirical analysis made over real-life ontologies, we show that our approach preserves significantly more of the original knowledge of the ontology than removing axioms

Conditional distributions of frame variables and voting behaviour in probability‐based surveys and opt‐in panels

Probability-based web surveys are increasingly challenged by decreasing response rates and high costs. A cheap and convenient solution is to use ‘opt-in’ online panels, which are based on non-probability samples. However, the quality of the data such panels produce is subject to debate. To improve our understanding in this regard, especially in the Swiss context, we compare conditional distributions of sociodemographic variables and voting behaviour of two probability-based web surveys and three opt-in panels. Indeed, point estimates in opt-in panels are well studied, but bivariate relationships between variables, arguably more important for researchers in political science research, have received less attention. Our analysis has the advantage of most variables of interest being included in the sampling frame and thus the true values are known for each conditional distribution. Our results show a lack of consistency and reproducibility in the results from opt-in panels, which leads us to recommend care when using this type of data

Asymmetric Incentives in Peer-to-Peer Systems

In most application scenarios for Peer-to-Peer systems, in order to achieve an overall acceptable system performance an incentive scheme is required that motivates users to share as much as possible of their free resources Today most peers use connections of asymmetric links, such as A-DSL or cable modems. Therefore, users have significantly more download bandwidth than their available upload bandwidth. Applying this observation to incentive schemes suggests that one unit of upload bandwidth should be valued higher than one download unit. Using such an incentive scheme leads the economy of the system to inflation. The incentive scheme would finally collapse. However, by exhibiting the phenomenon of altruistic behavior altruistic peers would accumulate the waste amount of the incentive units. Thus, inflation might be avoided. Gathering the results of a detailed simulative approach, this paper shows how to balance asymmetric incentive schemes in order to avoid inflation