de Sitter geodesics: reappraising the notion of motion

The de Sitter spacetime is transitive under a combination of translations and proper conformal transformations. Its usual family of geodesics, however, does not take into account this property. As a consequence, there are points in de Sitter spacetime which cannot be joined to each other by any one of these geodesics. By taking into account the appropriate transitivity properties in the variational principle, a new family of maximizing trajectories is obtained, whose members are able to connect any two points of the de Sitter spacetime. These geodesics introduce a new notion of motion, given by a combination of translations and proper conformal transformations, which may possibly become important at very-high energies, where conformal symmetry plays a significant role.Comment: 9 pages. V2: Presentation changes aiming at clarifying the text; version accepted for publication in Gen. Rel. Gra

Kinematics of a Spacetime with an Infinite Cosmological Constant

A solution of the sourceless Einstein's equation with an infinite value for the cosmological constant \Lambda is discussed by using Inonu-Wigner contractions of the de Sitter groups and spaces. When \Lambda --> infinity, spacetime becomes a four-dimensional cone, dual to Minkowski space by a spacetime inversion. This inversion relates the four-cone vertex to the infinity of Minkowski space, and the four-cone infinity to the Minkowski light-cone. The non-relativistic limit c --> infinity is further considered, the kinematical group in this case being a modified Galilei group in which the space and time translations are replaced by the non-relativistic limits of the corresponding proper conformal transformations. This group presents the same abstract Lie algebra as the Galilei group and can be named the conformal Galilei group. The results may be of interest to the early Universe Cosmology.Comment: RevTex, 7 pages, no figures. Presentation changes, including a new Title. Version to appear in Found. Phys. Let

Retrospective evaluations of sequences: Testing the predictions of a memory-based analysis

Retrospective evaluation (RE) of event sequences is known to be biased in various ways. The present paper presents a series of studies that examined the suggestion that the moments that are the most accessible in memory at the point of RE contribute to these biases. As predicted by this memory-based analysis, Experiment 1 showed that pleasantness ratings of word lists were biased by the presentation position of a negative item and by how easy the negative information was to retrieve. Experiment 2 ruled out the hypothesis that these findings were due to the dual nature of the task called upon. Experiment 3 further manipulated the memorability of the negative items – and corresponding changes in RE were as predicted. Finally, Experiment 4 extended the findings to more complex stimuli involving event narratives. Overall, the results suggest that assessments were adjusted based on the retrieval of the most readily available information

Torsion and the Gravitational Interaction

By using a nonholonomous-frame formulation of the general covariance principle, seen as an active version of the strong equivalence principle, an analysis of the gravitational coupling prescription in the presence of curvature and torsion is made. The coupling prescription implied by this principle is found to be always equivalent with that of general relativity, a result that reinforces the completeness of this theory, as well as the teleparallel point of view according to which torsion does not represent additional degrees of freedom for gravity, but simply an alternative way of representing the gravitational field.Comment: Version 2: minor presentation changes, a reference added, 11 pages (IOP style

Memory strategies mediate the relationships between memory and judgment

In the literature, the nature of the relationships between memory processes and summary evaluations is still a debate. According to some theoretical approaches (e.g., “two-memory hypothesis”; Anderson, 1989) retrospective evaluations are based on the impression formed while attending to the to-be assessed stimuli (on-line judgment) – no functional dependence between information retrieval and judgment is implied. Conversely, several theories entail that judgment must depend, at least in part, on memory processes (e.g., Dougherty, Gettys, & Ogden, 1999; Schwarz, 1998; Tversky & Kahneman, 1973). The present study contributes to this debate by addressing two important issues. First, it shows how more comprehensive memory measures than those used previously (e.g., Hastie & Park, 1986) are necessary in order to detect a relationship between memory and retrospective evaluations. Secondly, it demonstrates how memory strategies influence the relationship between memory and judgment. Participants recalled lists of words, after having assessed each of them for their pleasantness. Results showed a clear association between memory and judgment, which was mediated by the individual strategies participants used to recall the items

P02-07. High Concentrations of Interleukin-15 and Low Concentrations of CCL5 in Breast Milk are Associated with Protection against Postnatal HIV Transmission

Background: Natural variations in IL-15 concentration have not been investigated for an association with an immune-protection against HIV. Given IL-15's central role in anti-HIV immunity, we hypothesized that higher concentrations of IL-15 in breast milk may protect against postnatal mother-to-child HIV transmission. Methods: In a case-control study nested within a clinical trial in Zambia, we compared IL-15 concentrations in breast milk of 22 HIV-infected women who transmitted HIV to their infants through breastfeeding with those of 72 who did not, as well as 18 HIV-uninfected women. Breast milk HIV RNA quantity, sodium, CXCL12, CCL5, and IL-8 concentrations were measured as well as maternal plasma HIV RNA concentrations and CD4 cell count. We used logistic regression modeling to adjust for potential confounders. Results: Higher concentrations of IL-15 in breast milk (adjusted odds ratio [AOR]: 0.01 per log10 pg/ml increase, 95% confidence interval [CI]: <0.001 to 0.3) were associated with protection against postnatal HIV transmission in univariate analysis and after adjusting for maternal CD4 cell counts, breast milk HIV RNA, CCL5, CXCL12, and IL-8 concentrations. Breast milk IL-15 concentration correlated with breast milk sodium, the other cytokines and HIV RNA concentration. It was inversely correlated with infant birth weight and tended to be higher in 1 week than in 1 month post-partum samples. Breast milk CCL5 concentrations were associated with increased risk of HIV transmission (AOR: 12.7 95% CI: 1.6 to 102.0) in adjusted analysis. Breast milk CXCL12 and IL-8 concentrations were not independently associated with transmission. Conclusion: High concentration of IL-15 were associated with a protection against breastfeeding HIV transmission after adjusting for other pro-inflammatory cytokines, HIV RNA in breast milk, and maternal CD4 cell count. These results corroborate a protective role of IL-15-mediated cellular immunity against HIV transmission during breastfeeding. They are informative for vaccination studies using IL-15 as an adjuvant

An effect of semantic memory on immediate memory in the visual domain

The present study extends the findings of Hemmer and Steyvers (2009a) by investigating the influence of semantic memory on short-term visual memory. In an experiment we tested how prior knowledge moderates serial position effects, using familiar (vegetables) and non-familiar stimuli (random shapes). Participants (Ps) saw lists of six images; each list held images of vegetables or random shapes. Immediately after list presentation, one of the items was presented again, in a new, randomly determined size. Ps were asked to resize the image so that it was as close as possible to the size of the just presented item. Results showed that, for the familiar items (vegetables), memory for the item’s size was supported by prior knowledge of the normal size of the objects; this was not the case for the random shapes. Moreover, there was a stronger serial position effect for random shapes than vegetables suggesting that for the serial positions where memory is typically lowest, the serial position effect was moderated through the support from long-term knowledge

Retrospective and prospective evaluations of mammography screening narratives: The role of own experience

We investigated the role of previous experience when providing summary judgments of mammography narratives. A total of 807 women who either did or did not have previous experience of a mammogram were presented with a written description of a mammography visit. We manipulated the presentation position of a negative element within the narrative to alter its accessibility in memory and determine whether the latter impacted equally on two types of summary judgments. After the narrative presentation, participants were asked to provide both retrospective and prospective evaluations, that is, summary judgments about the described event and an appraisal of the likelihood of participating in future instances of such event, respectively. A recency effect was observed only for retrospective but not for prospective evaluations. When examined only for the subset of women who had undergone a mammography visit themselves, prospective evaluations were shown to be predicted by the reported quality of the mammography participants experienced themselves. The findings support and extend the accessibility model of emotional self-report and suggest that own experience leaks into evaluations of hypothetical scenarios by selectively impacting on prospective evaluations

Consistent Gravitationally-Coupled Spin-2 Field Theory

Inspired by the translational gauge structure of teleparallel gravity, the theory for a fundamental massless spin-2 field is constructed. Accordingly, instead of being represented by a symmetric second-rank tensor, the fundamental spin-2 field is assumed to be represented by a spacetime (world) vector field assuming values in the Lie algebra of the translation group. The flat-space theory naturally emerges in the Fierz formalism and is found to be equivalent to the usual metric-based theory. However, the gravitationally coupled theory, with gravitation itself described by teleparallel gravity, is shown not to present the consistency problems of the spin-2 theory constructed on the basis of general relativity.Comment: 16 pages, no figures. V2: Presentation changes, including addition of a new sub-section, aiming at clarifying the text; version accepted for publication in Class. Quantum Grav

Social norms and rank-based nudging: Changing willingness to pay for healthy food

People's evaluations in the domain of healthy eating are at least partly determined by the choice context. We systematically test reference level and rank-based models of relative comparisons against each other and explore their application to social norms nudging, an intervention that aims at influencing consumers' behavior by addressing their inaccurate beliefs about their consumption relative to the consumption of others. Study 1 finds that the rank of a product or behavior among others in the immediate comparison context, rather than its objective attributes, influences its evaluation. Study 2 finds that when a comparator is presented in isolation the same rank-based process occurs based on information retrieved from memory. Study 3 finds that telling people how their consumption ranks within a normative comparison sample increases willingness to pay for a healthy food by over 30% relative to the normal social norms intervention that tells them how they compare to the average. We conclude that social norms interventions should present rank information (e.g., "you are in the most unhealthy 10% of eaters") rather than information relative to the average (e.g., "you consume 500 calories more than the average person")