When good theories make bad predictions

Chaos-related obstructions to predictability have been used to challenge accounts of theory validation based on the agreement between theoretical predictions and experimental data (Rueger & Sharp, 1996. The British Journal for the Philosophy of Science, 47, 93–112; Koperski, 1998. Philosophy of Science, 40, 194–212). These challenges are incomplete in two respects: (a) they do not show that chaotic regimes are unpredictable in principle (i.e., with unbounded resources) and, as a result, that there is something conceptually wrong with idealized expectations of correct predictions from acceptable theories, and (b) they do not explore whether chaos-induced predictive failures of deterministic models can be remedied by stochastic modeling. In this paper we appeal to an asymptotic analysis of state space trajectories and their numerical approximations to show that chaotic regimes are deterministically unpredictable even with unbounded resources. Additionally, we explain why stochastic models of chaotic systems, while predictively successful in some cases, are in general predictively as limited as deterministic ones. We conclude by suggesting that the way in which scientists deal with such principled obstructions to predictability calls for a more comprehensive approach to theory validation, on which experimental testing is augmented by a multifaceted mathematical analysis of theoretical models, capable of identifying chaos-related predictive failures as due to principled limitations which the world itself imposes on any less-than-omniscient epistemic access to some natural systems. We give special thanks to two anonymous reviewers for their helpful comments that have substantially contributed to the final version of this paper     

Intersections Between Nativity, Ethnic Density, and Neighborhood SES: Using an Ethnic Enclave Framework to Explore Variation in Puerto Ricans’ Physical Health

Although past research has demonstrated a “health disadvantage” for Puerto Rican adults, very little is known about correlates of health among this group. Given Puerto Ricans’ unique experiences of migration and settlement, an ethnic enclave framework that integrates nativity, ethnic density, and neighborhood SES may offer insight into factors influencing Puerto Ricans’ health. This study uses a sample of 449 adult mainland- and island-born Puerto Ricans living in New York City and Chicago. The data, collected as a part of the MIDUS Survey of Minority Groups, are stratified by neighborhood ethnic density and neighborhood SES, allowing for the examination of the individual and joint influences of neighborhood characteristics on physical health. Results revealed that ethnic density and neighborhood SES were not independently or interactively related to physical health for mainland-born Puerto Ricans. However, the interaction between ethnic density and neighborhood SES was related to self-reported health, functional limitations, and health symptoms for island-born Puerto Ricans. Island-born Puerto Ricans living in ethnically dense, low SES neighborhoods reported worse health than island-born Puerto Ricans living in other types of neighborhoods. This may be a result of isolation from resources both within and outside the neighborhood.     

Early effects of neighborhood density and phonotactic probability of spoken words on event-related potentials

All current models of spoken word recognition propose that sound-based representations of spoken words compete with, or inhibit, one another during recognition. In addition, certain models propose that higher probability sublexical units facilitate recognition under certain circumstances. Two experiments were conducted examining ERPs to spoken words and nonwords simultaneously varying in phonotactic probability and neighborhood density. Results showed that the amplitude of the P2 potential was greater for high probability-density words and nonwords, suggesting an early inhibitory effect of neighborhood density. In order to closely examine the role of phonotactic probability, effects of initial phoneme frequency were also examined. The latency of the P2 potential was shorter for words with high initial-consonant probability, suggesting a facilitative effect of phonotactic probability. The current results are consistent with findings from previous studies using reaction time and eye-tracking paradigms and provide new insights into the time-course of lexical and sublexical activation and competition.     

A Dual Process Model of Attitudes towards Immigration: Person × Residential Area Effects in a National Sample

This research took a person × situation approach to predicting prejudice by looking at how social worldviews interact with real‐world environmental factors to predict how people respond to immigrants within their local area. Taking a Dual Process Motivational approach, we hypothesized that a higher proportion of immigrants in the local community would be associated with negative attitudes toward immigration for respondents high in dangerous world beliefs. Conversely, we hypothesized that living in a highly affluent (as opposed to socioeconomically deprived) community would be associated with negative attitudes toward immigration for respondents high in competitive world beliefs. Both hypotheses were supported using regional information derived from national census data combined with representative survey data from a large telephone sample conducted in New Zealand (N = 6,489). These findings support the proposition that individual differences interact with specific features of the environment to predict people's levels of prejudice in distinct ways.     

Toward an understanding of aging in plutonium from direct measurements of stored energy

ABSTRACT

We present here the first direct measurement of the radiation-damage-induced energy stored in δ-phase plutonium. The primary mode of radioactive decay of ²³⁹Pu occurs with a time constant of τ=1.1?×?10¹²?s. Each decay imparts about 85?keV of recoil energy to the uranium byproduct, 5.2?Mev to the alpha particle, and a spectrum of mostly low energy gamma rays with the most probable at 51?keV [1]. Most of the decay energy is converted immediately to heat, releasing about 1.9?mW/g. However, some thermally-recoverable energy remains trapped. Reported here are measurements of that stored energy using differential scanning calorimetry (DSC) applied to ²³⁹Pu-2.0 at.%Ga δ-phase alloy. Retained energy of ～2 J/g saturates at about 5 months and is unchanged after 30 years. The magnitude of the stored energy agrees with a short-bond defect model that that we present here. This model treats radiation damage as a Pu impurity with shortened bond lengths. It explains the change in known properties with age and predicts that density increases with age, contrary to current thinking. The short-bond impurities proposed are expected to act like other impurities, affecting strength, phase transitions, grain boundaries and other metallurgical properties.     

After Novelty: The Mundane Practices of Ensuring a Safe and Stable Supply of Bone

New medical technologies to a great extent use material from human bodies as therapeutic tools. Social science studies of such ‘tools’ have tended to focus on technologies associated with novelty and drama. This paper, in contrast, concerns an old, well-entrenched and ostensibly undramatic technology, bone transfers, that has only recently gained public attention. The history of bone transplants is intertwined with a desire for a safe and stable supply of bone. This desire has a number of rarely debated social implications of relevance to transplant medicine in general: the gradual industrialization of procurement; the institutional production of the view of the body as a dividable resource; the emergence of a notion of scarcity; of body parts as waste; of death as a productive moment in which body parts acquire potential exchange value; and of tensions between an ethics of respect for donors and an ethics of efficient procurement. Historical analysis combined with a contemporary phenomenological approach suggests that the ‘newness’ typically associated with usage of human biological material is not related to transplant technologies as a medical discipline as such, but rather to changes in its social organization and features of the everyday experience of living with the transplant technologies.     

Phonological neighbourhood effects in French spoken-word recognition

According to activation-based models of spoken-word recognition, words with many and high-frequency phonological neighbours are processed more slowly than words with few and low-frequency phonological neighbours. Although considerable empirical support for inhibitory neighbourhood density effects has accumulated, especially in English, little or nothing is known about the effects of neighbourhood frequency and its interaction with neighbourhood density. In this study we examine both effects first separately and then simultaneously in French lexical decision experiments. As in English, we found that words in dense neighbourhoods are recognized more slowly than words in sparse neighbourhoods. Moreover, we showed that words with higher frequency neighbours are processed more slowly than words with no higher frequency neighbours, but only for words occurring in sparse neighbourhoods. Implications of these results for spoken-word recognition models are discussed.     

Making the uncontrollable seem controllable: The role of action in the illusion of control

It is well known that certain variables can bias judgements about the perceived contingency between an action and an outcome, making them depart from the normative predictions. For instance, previous studies have proven that the activity level or probability of responding, P(R), is a crucial variable that can affect these judgements in objectively noncontingent situations. A possible account for the P(R) effect is based on the differential exposure to actual contingencies during the training phase, which is in turn presumably produced by individual differences in participants' P(R). The current two experiments replicate the P(R) effect in a free-response paradigm, and show that participants' judgements are better predicted by P(R) than by the actual contingency to which they expose themselves. Besides, both experiments converge with previous empirical data, showing a persistent bias that does not vanish as training proceeds. These findings contrast with the preasymptotic and transitory effect predicted by several theoretical models.     

First principles study of the temperature-dependent elastic properties of W

The temperature-dependent elastic constants of body-centred cubic (bcc) phase W are presented from first principles quasi-static approach. With the quasi-harmonic approximation model, the Hugoniot equation of state and temperature-dependence linear thermal expansion coefficient is successfully obtained. The adiabatic elastic constants show a normal behaviour with temperature: decrease with increasing temperature. Based on the obtained adiabatic elastic constants, the structural stability and polycrystalline aggregate properties including bulk modulus B, shear modulus G, and B/G ratio are analysed for bcc phase W. In addition, the sound velocities as a function of temperature for bcc phase W are predicted.     

Revisiting the level-of-service framework for pedestrian comfortability: Velocity depicts more accurate perceived congestion than local density

The evaluation of pedestrian comfortability is important for the construction and management of walkable spaces. Pedestrian level-of-service (LOS), which is mostly categorized by density, has been widely applied and is believed to be capable of indicating the comfortability of the crowd. However, there is a lack of evidence that physically measured LOS reflects psychological comfortability, let alone the comparison between the performances of different candidate indicators, including the velocity and different local densities. Here, we show that walking velocity depicts pedestrian perceived congestion more accurately than density. In our experiments on pedestrians in a room-egress scenario with an inner obstacle, we obtained objective physical trajectory data from video analysis as well as subjective perception data from a questionnaire survey. The performance of the velocity and four types of local densities in reproducing pedestrian perceptions were numerically evaluated. We found that the velocity outperformed the local density. The lower performance of local densities was mainly caused by the pedestrians located at the back of the crowd, who walked at lower velocities and perceived higher congestion, despite their lower local densities that would correspond to less crowdedness from a physical viewpoint. Besides, the perceived congestion of pedestrians was shown to be affected by the initial pedestrian positions at the crowd, the obstacle layout, and the pedestrians’ age and gender. Furthermore, we suggest that the larger the gap between the desired and actual velocities, the larger the extent of the perceived congestion. We expect that our findings will contribute to a more accurate evaluation of pedestrian comfortability, which could help improve the walkable spaces of various infrastructures.