Chaotic, memory, and cooling rate effects in spin glasses: Evaluation of the Edwards-Anderson model

We investigate chaotic, memory, and cooling rate effects in the three-dimensional Edwards-Anderson model by doing thermoremanent (TRM) and ac susceptibility numerical experiments and making a detailed comparison with laboratory experiments on spin glasses. In contrast to the experiments, the Edwards-Anderson model does not show any trace of reinitialization processes in temperature change experiments (TRM or ac). A detailed comparison with ac relaxation experiments in the presence of dc magnetic field or coupling distribution perturbations reveals that the absence of chaotic effects in the Edwards-Anderson model is a consequence of the presence of strong cooling rate effects. We discuss possible solutions to this discrepancy, in particular the smallness of the time scales reached in numerical experiments, but we also question the validity of the Edwards-Anderson model to reproduce the experimental results.

Entropy change and magnetocaloric effect in Gd5(SixGe1-x)4

Isothermal magnetization curves up to 23 T have been measured in Gd5Si1.8Ge2.2. We show that the values of the entropy change at the first-order magnetostructural transition, obtained from the Clausius-Clapeyron equation and the Maxwell relation, are coincident, provided the Maxwell relation is evaluated only within the transition region and the maximum applied field is high enough to complete the transition. These values are also in agreement with the entropy change obtained from differential scanning calorimetry. We also show that a simple phenomenological model based on the temperature and field dependence of the magnetization accounts for these results.

Evidence for oxygen-island formation on Al(111): Cluster-model theory and x-ray photoelectron spectroscopy

The O 1s x-ray photoelectron spectroscopy spectrum for Al(111)/O at 300 K shows two components whose behavior as a function of time and variation of detection angle are consistent with either (a) a surface species represented by the higher binding-energy (BE) component and a subsurface species represented by the lower BE component, or (b) small close-packed oxygen islands with the interior atoms represented by the lower BE component and the perimeter atoms by the higher BE component. We have modeled both situations using ab initio Hartree-Fock wave functions for clusters of Al and O atoms. For an O atom in a threefold site, it was found that a below-surface position gave a higher O 1s BE than an above-surface position, incompatible with interpretation (a). This change in the O 1s BE could arise because the bond for O to Al may have a more covalent character when the O is below the surface than when it is above the surface. We present evidence consistent with this view. An O adatom island with all the O atoms in threefold sites gives calculated O 1s BE's which are significantly higher for the perimeter O atoms. Further, the results for an isolated O island without the Al substrate present also give higher BE¿s for the perimeter atoms. Both these results are consistent with interpretation (b). Published scanning-tunneling-microscopy data supports the suggestion that the chemisorbed state consists of small, close-packed islands, whereas the presence of two vibrational modes in high-resolution electron-energy-loss spectroscopy data has been interpreted as representing surface and subsurface oxygen atoms. In light of the present results, we suggest that a vibrational interpretation in terms of interior and perimeter adatoms should be considered.

Technological Change and Immigration

We develop a simple model where two technologies are available to produce the same good, and we study under what conditions both will be used. We use the model to analyze the consequences of the simultaneous use of two different technologies for the economic variables and economic growth. Finally, we explore how migrations of factors affect the technological change and the performance of the economy.

Estimating slope and level change in N=1 designs

The current study proposes a new procedure for separately estimating slope change and level change between two adjacent phases in single-case designs. The procedure eliminates baseline trend from the whole data series prior to assessing treatment effectiveness. The steps necessary to obtain the estimates are presented in detail, explained, and illustrated. A simulation study is carried out to explore the bias and precision of the estimators and compare them to an analytical procedure matching the data simulation model. The experimental conditions include two data generation models, several degrees of serial dependence, trend, level and/or slope change. The results suggest that the level and slope change estimates provided by the procedure are unbiased for all levels of serial dependence tested and trend is effectively controlled for. The efficiency of the slope change estimator is acceptable, whereas the variance of the level change estimator may be problematic for highly negatively autocorrelated data series.

Cities, skills, and regional change

One approach to urban areas emphasizes the existence of certain immutable relationships, such as Zipf's or Gibrat's Law. An alternative view is that urban changereflects individual responses to changing tastes or technologies. This paper examinesalmost 200 years of regional change in the U.S. and finds that few, if any, growth relationships remain constant, including Gibrat's Law. Education does a reasonable jobof explaining urban resilience in recent decades, but does not seem to predict countygrowth a century ago. After reviewing this evidence, we present and estimate a simple model of regional change, where education increases the level of entrepreneurship.Human capital spillovers occur at the city level because skilled workers produce moreproduct varieties and thereby increase labor demand. We find that skills are associatedwith growth in productivity or entrepreneurship, not with growth in quality of life, atleast outside of the West. We also find that skills seem to have depressed housing supplygrowth in the West, but not in other regions, which supports the view that educatedresidents in that region have fought for tougher land-use controls. We also present evidence that skills have had a disproportionately large impact on unemployment duringthe current recession.

La Formación de la imagen turística inducida: un modelo conceptual

Teniendo en cuenta que la imagen turística ha sido reconocida como uno de los elementos más influyentes para la competitividad de los destinos turísticos, el principal objetivo de este artículo es construir un marco conceptual que muestre la influencia de la red relacional del destino en su imagen emitida. En este contexto, se asume que la imagen tu rística es una construcción social resultante de lainteracción de los distintos agentes que intervienen en el destino turístico (administraciones públicas, instituciones locales, empresas turísticas, etc.); y se propone un modelo teórico para mostrar los efectos de la red relacional del destino turístico en la calidad de la imagen turística creada en términos de conocimiento generado y, por tanto, en su competitividad

The global welfare impact of China: Trade integration and technological change

This paper evaluates the global welfare impact of China's trade integration and technological change in a multi-country quantitative Ricardian-Heckscher-Ohlin model.We simulate two alternative growth scenarios: a "balanced" one in which China's productivity grows at the same rate in each sector, and an "unbalanced" one in whichChina's comparative disadvantage sectors catch up disproportionately faster to theworld productivity frontier. Contrary to a well-known conjecture (Samuelson 2004),the large majority of countries experience significantly larger welfare gains whenChina's productivity growth is biased towards its comparative disadvantage sectors.This finding is driven by the inherently multilateral nature of world trade.

Demand-based structural change and balanced economic growth

[eng] We analyze the equilibrium of a multi-sector exogenous growth model where the introduction of minimum consumption requirements drives structural change. We show that equilibrium dynamics simultaneously exhibt structural change and balanced growth of aggregate variables as is observed in US when the initial intensity of minimum consumption requirements is sufficiently small. This intensity is measured by the ratio between the aggregate value of the minimum consumption requirements and GDP and, therefore, it is inversely related with the level of economic development. Initially rich economies benefit from an initially low intensity of the minimum consumption requirements and, as a consequence, these economies end up exhibiting balanced growth of aggregate variables, while there is structural change. In contrast, initially poor economies suffer from an initially large intensity of the minimum consumption requirements, which makes the growth of the aggregate variables unbalanced during a very large period. These economies may never exhibit simultaneously balanced growth of aggregate variables and structural change.

Monte Carlo study of a kinetic lattice model with random diffusion of disorder

We report Monte Carlo results for a nonequilibrium Ising-like model in two and three dimensions. Nearest-neighbor interactions J change sign randomly with time due to competing kinetics. There follows a fast and random, i.e., spin-configuration-independent diffusion of Js, of the kind that takes place in dilute metallic alloys when magnetic ions diffuse. The system exhibits steady states of the ferromagnetic (antiferromagnetic) type when the probability p that J>0 is large (small) enough. No counterpart to the freezing phenomena found in quenched spin glasses occurs. We compare our results with existing mean-field and exact ones, and obtain information about critical behavior.

Observation of a continuous interior crisis in the Hindmarsh-Rose neuron model.

Interior crises are understood as discontinuous changes of the size of a chaotic attractor that occur when an unstable periodic orbit collides with the chaotic attractor. We present here numerical evidence and theoretical reasoning which prove the existence of a chaos-chaos transition in which the change of the attractor size is sudden but continuous. This occurs in the Hindmarsh¿Rose model of a neuron, at the transition point between the bursting and spiking dynamics, which are two different dynamic behaviors that this system is able to present. Moreover, besides the change in attractor size, other significant properties of the system undergoing the transitions do change in a relevant qualitative way. The mechanism for such transition is understood in terms of a simple one-dimensional map whose dynamics undergoes a crossover between two different universal behaviors

Estratigrafia i evolució conceptual d'un paisatge de muntanya al massís del Garraf: la Maçana-Rovirós-Térmens (Begues)

En aquest estudi, l'aplicació regressiva de tècniques com la prospecció arqueològica, la foto i cartointerpretació, els SIG i el buidatge documental han permès la reconstrucció diacrònica del paisatge de l'àrea de la Maçana-Térmens-Rovirós (Begues). L'estudi paisatgístic del Garraf revesteix un singular interès per la seva condició muntanyenca i la seva intensa antropització. Els entorns de muntanya són medis especialment sensibles a processos de canvi, especialment en el cas del massís del Garraf, proper a importants nuclis d'habitació des de l'antiguitat. El nostre treball mostrarà com, en ocasions, el canvi paisatgístic ha estat irreversible al massís.

Integration in strategic alliances : a conceptual framework of IT use in marketing as NPD key factor

En una economia basada en el coneixement, la innovació del producte es considera un factor clau a l'hora de determinar la competitivitat, la productivitat i el creixement d'una companyia. No obstant això, l'experiència de les companyies demostra la necessitat d'un nou model de gestió de la innovació del producte: una gestió basada en el màrqueting, en què la cooperació i l'ús intensiu de les tecnologies de la informació i de la comunicació (TIC) són especialment importants. En els darrers anys, la bibliografia sobre màrqueting ha analitzat el paper de la cooperació en l'èxit del procés d'innovació. No obstant això, fins ara pocs treballs han estudiat el paper que té l'ús de les TIC en el màrqueting en l'èxit del desenvolupament de nous productes (NPD, New Product Development en anglès). És una omissió curiosa, tenint en compte que el nou entorn competitiu és definit per una economia i una societat basades principalment en l'ús intensiu de les TIC i del coneixement. L'objectiu d'aquest treball és investigar el paper que l'ús de les TIC en el màrqueting té en el procés de desenvolupament de nous productes, com a element que reforça la integració d'agents al projecte, afavorint l'establiment de relacions dirigides a la cooperació i l'adquisició d'intel·ligència de mercat útil en el procés de desenvolupament de nous productes. L'estudi d'una mostra de 2.038 companyies de tots els sectors de l'activitat econòmica a Catalunya ens permet contrastar hipòtesis inicials i establir un perfil de companyia innovadora basat en les importants relacions que hi ha entre la innovació, l'ús de TIC en el màrqueting i la integració. Sobresurten dues idees en la nostra anàlisi. En primer lloc, l'ús intensiu de les TIC en el màrqueting fa que la companyia sigui més innovadora, ja que percep que el seu ús ajuda a superar barreres a la innovació i accelera els processos, que es tornen més eficients. En segon lloc, incrementant l'ús de les TIC en el màrqueting es fa augmentar la predisposició de la companyia a integrar agents particulars en l'entorn de negoci en el desenvolupament del procés d'innovació i a col·laborar-hi, de manera que es millora el grau d'adaptació del nou producte a les demandes del mercat.

Numerical analysis of including phase change material in a domestic hot water cylinder

The domestic hot water cylinder incorporates encapsulated pcm placed in 57 vertical pipes. The use of PCM increases the thermal energy storage capacity of the cylinder and allows the use of low cost electricity during low peak periods. After experimental validation the numerical model developed in the project will be used to optimize the distribution of the pcm inside the water tank.

Collaborative explicit plasticity framework: a conceptual scheme for the generation of plastic and group-aware user interfaces

The advent of new advances in mobile computing has changed the manner we do our daily work, even enabling us to perform collaborative activities. However, current groupware approaches do not offer an integrating and efficient solution that jointly tackles the flexibility and heterogeneity inherent to mobility as well as the awareness aspects intrinsic to collaborative environments. Issues related to the diversity of contexts of use are collected under the term plasticity. A great amount of tools have emerged offering a solution to some of these issues, although always focused on individual scenarios. We are working on reusing and specializing some already existing plasticity tools to the groupware design. The aim is to offer the benefits from plasticity and awareness jointly, trying to reach a real collaboration and a deeper understanding of multi-environment groupware scenarios. In particular, this paper presents a conceptual framework aimed at being a reference for the generation of plastic User Interfaces for collaborative environments in a systematic and comprehensive way. Starting from a previous conceptual framework for individual environments, inspired on the model-based approach, we introduce specific components and considerations related to groupware.