The influence of the precipitation rate on the properties of porous chromia

The properties were studied of heated (320°C) chromia samples, prepared by two precipitation methods: \ud \ud 1. (1) addition of ammonia to chromium salt solutions,\ud 2. (2) OH− formation in chromium salt solutions through hydrolysis of urea.\ud \ud Samples formed by means of the first method are macro or mesoporous and have a lower specific surface area (~200 m2·g−1) than those formed by urea hydrolysis (~300 m2·g−1). Only in the case of a very slow addition of the ammonia solution these properties of the chromia's become equal. Experiments show that the micro porous type samples with high surface area are only formed if the pH range 5.1 to 5.7 is passed slowly. The formation of polychromium complexes of uniform size is suggested.\ud \u

Trio-One: Layering Uncertainty and Lineage on a Conventional DBMS

Trio is a new kind of database system that supports data, uncertainty, and lineage in a fully integrated manner. The first Trio prototype, dubbed Trio-One, is built on top of a conventional DBMS using data and query translation techniques together with a small number of stored procedures. This paper describes Trio-One's translation scheme and system architecture, showing how it efficiently and easily supports the Trio data model and query language

Evolving Symbolic Controllers

International audienceThe idea of symbolic controllers tries to bridge the gap between the top-down manual design of the controller architecture, as advocated in Brooks' subsumption architecture, and the bottom-up designer-free approach that is now standard within the Evolutionary Robotics community. The designer provides a set of elementary behavior, and evolution is given the goal of assembling them to solve complex tasks. Two experiments are presented, demonstrating the efficiency and showing the recursiveness of this approach. In particular, the sensitivity with respect to the proposed elementary behaviors, and the robustness w.r.t. generalization of the resulting controllers are studied in detail

Robust Price of Anarchy for Atomic Games with Altruistic Players

We study the inefficiency of equilibria for various classes of games when players are (partially) altruistic. We model altruistic behavior by assuming that player i's perceived cost is a convex combination of 1-\beta_i times his direct cost and \beta_i times the social cost. Tuning the parameters \beta_i allows smooth interpolation between purely selfish and purely altruistic behavior. Within this framework, we study altruistic extensions of linear congestion games, fair cost-sharing games and valid utility games. We derive (tight) bounds on the price of anarchy of these games for several solution concepts. Thereto, we suitably adapt the smoothness notion introduced by Roughgarden and show that it captures the essential properties to determine the robust price of anarchy of these games. Our bounds reveal that for congestion games and cost-sharing games the worst-case robust price of anarchy increases with increasing altruism, while for valid utility games it remains constant and is not affected by altruism. We also show that the increase in price of anarchy is not a universal phenomenon: for symmetric singleton linear congestion games we derive a bound on the price of anarchy for pure Nash equilibria that decreases as the level of altruism increases. Since the bound is also strictly lower than the robust price of anarchy, it exhibits a natural example in which Nash equilibria are more efficient than more permissive notions of equilibrium

Variational method for learning Quantum Channels via Stinespring Dilation on neutral atom systems

The state $|\psi(t)\rangle$ of a closed quantum system evolves under the Schr\"{o}dinger equation, where the reversible evolution of the state is described by the action of a unitary operator $U(t)$ on the initial state $|\psi_0\rangle$, i.e.\ $|\psi(t)\rangle=U(t)|\psi_0\rangle$. However, realistic quantum systems interact with their environment, resulting in non-reversible evolutions, described by Lindblad equations. The solution of these equations give rise to quantum channels $\Phi_t$ that describe the evolution of density matrices according to $\rho(t)=\Phi_t(\rho_0)$, which often results in decoherence and dephasing of the state. For many quantum experiments, the time until which measurements can be done might be limited, e.g. by experimental instability or technological constraints. However, further evolution of the state may be of interest. For instance, to determine the source of the decoherence and dephasing, or to identify the steady state of the evolution. In this work, we introduce a method to approximate a given target quantum channel by means of variationally approximating equivalent unitaries on an extended system, invoking the Stinespring dilation theorem. We report on an experimentally feasible method to extrapolate the quantum channel on discrete time steps using only data on the first time steps. Our approach heavily relies on the ability to spatially transport entangled qubits, which is unique to the neutral atom quantum computing architecture. Furthermore, the method shows promising predictive power for various non-trivial quantum channels. Lastly, a quantitative analysis is performed between gate-based and pulse-based variational quantum algorithms.Comment: 11 pages, 7 figure

Influence of atmosphere, interparticle distance and support on the stability of silver on α-alumina for ethylene epoxidation

The stability of supported metal particles is an important parameter in heterogenous catalysis. For silver catalysts supported on α-alumina, industrially used in ethylene epoxidation, the loss of silver surface area as result of particle growth is one of the most important deactivation mechanisms. In this work, the growth of silver particles was investigated by exposing catalysts to thermal treatments. The presence of oxygen during heating strongly enhanced particle growth, and the interparticle distance was a crucial parameter. However, restricting movement of complete silver particles using cage-like α-alumina did not limit particle growth. These findings indicate that Ostwald ripening was the dominant mechanism behind particle growth, with the diffusion of oxidized silver species being a rate limiting factor. Finally, higher surface area α-alumina provided better silver stability during ethylene epoxidation, with only limited decrease in selectivity. This makes silver supported on high surface area α-alumina promising candidates for ethylene epoxidation catalysis

ParaDisEO-Based Design of Parallel and Distributed Evolutionary Algorithms

The original publication is available at www.springerlink.comInternational audienceParaDisEO is a framework dedicated to the design of parallel and distributed metaheuristics including local search methods and evolutionary algorithms. This paper focuses on the latter aspect. We present the three parallel and distributed models implemented in ParaDisEO and show how these can be exploited in a user-friendly, flexible and transparent way. These models can be deployed on distributed memory machines as well as on shared memory multi-processors, taking advantage of the shared memory in the latter case. In addition, we illustrate the instantiation of the models through two applications demonstrating the efficiency and robustness of the framework