A Definition of Metastability for Markov Processes with Detailed Balance

A definition of metastable states applicable to arbitrary finite state Markov processes satisfying detailed balance is discussed. In particular, we identify a crucial condition that distinguishes genuine metastable states from other types of slowly decaying modes and which leads to properties similar to those postulated in the restricted ensemble approach \cite{pen71}. The intuitive physical meaning of this condition is simply that the total equilibrium probability of finding the system in the metastable state is negligible. As a concrete application of our formalism we present preliminary results on a 2D kinetic Ising model.Comment: 5 pp. 1 Figure, presented in News, Expectations and Trends in Statistical Physics-3rd International Conference, 13-18 August 2005, Kolymbari Cret

Quantitative determination of engine water ingestion

A nonintrusive optical technique is described for determination of liquid mass flux in a droplet laden airstream. The techniques were developed for quantitative determination of engine water ingestion resulting from heavy rain or wheel spray. Independent measurements of the liquid water content (LWC) of the droplet laden airstream and of the droplet velocities were made at the stimulated nacelle inlet plane for the liquid mass flux determination. The LWC was measured by illuminating and photographing the droplets contained within a thin slice of the flow field by means of a sheet of light from a pulsed laser. A fluorescent dye introduced in the water enchanced the droplet image definition. The droplet velocities were determined from double exposed photographs of the moving droplet field. The technique was initially applied to a steady spray generated in a wind tunnel. It was found that although the spray was initially steady, the aerodynamic breakup process was inherently unsteady. This resulted in a wide variation of the instantaneous LWC of the droplet laden airstream. The standard deviation of ten separate LWC measurements was 31% of the average. However, the liquid mass flux calculated from the average LWC and droplet velocities came within 10% of the known water ingestion rate

On booms that never bust: ambiguity in experimental asset markets with bubbles

We study the effect of ambiguity on the formation of bubbles and crashes in experimental asset markets à la Smith, Suchanek, and Williams (1988) by allowing for ambiguity in the fundamental value of the asset. Although bubbles form in both the ambiguous and the risky environments we find that asset prices tend to be lower when the fundamental value is ambiguous than when it is risky. Bubbles do not crash in the ambiguous case whereas they do so in the risky one. These findings, regarding depressed prices and the absence of crashes in the presence of ambiguity, are in line with recent theoretical work stressing the crucial role of ambiguity to account for surprisingly low equity prices (high returns) as well as herding in asset markets

Antiferromagnetic spin chain behavior and a transition to 3D magnetic order in Cu(D,L-alanine)2: Roles of H-bonds

We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2.H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0 = (-2.12 $\pm$ 0.08) cm$^{-1}$, between neighbor coppers at 4.49 {\AA} along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0 = (-2.27 $\pm$ 0.02) cm$^{-1}$ and g = 2.091 $\pm$ 0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 {\AA} are estimated within the range 0.1 < |2J1| < 0.4 cm$^{-1}$, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain interactions.Comment: 10 pages, 4 figure

Payment Scheme Self-Selection in the Credence Goods Market: An Experimental Study

Given heterogeneity in expert behavior across payment schemes in credence goods markets, it becomes important to understand the consequences of payment scheme selection. To study the effect on customer well being of expert self-selection, we recruited subjects to participate in a real-effort credence good laboratory market. Experts were either randomly assigned or faced with the choice of three payment schemes: fee-for-service, salary, and capitation. We found that experts who selected fee-for-service payment resulted in customers with significantly worse outcomes in comparison with experts who had been randomly assigned to fee-for-service. In contrast, experts who selected salary payment did not change customer outcomes relative to those who were randomly assigned

CUESTOR: Una nueva aproximación integral a la evaluación automática de prácticas de programación

A pesar de que existen diversas aproximaciones para la evaluación automática de prácticas de programación, su aplicación fuera de los entornos en que fueron diseñados no siempre es posible. En este trabajo se presenta una nueva plataforma abierta que proporciona los mecanismos necesarios para realizar una evaluación completa de un ejercicio de programación realizado en C o en Java. Este proceso de evaluación incluye la verificación del cumplimiento de los requisitos especificados, el método de resolución, la calidad del código fuente y la comprobación del plagio. El funcionamiento de cada uno de los componentes de evaluación ha sido verificado de forma exhaustiva mediante la utilización de las entregas realizadas por los alumnos en años anteriores.Peer Reviewe