Covariation, Structure and Generalization: Building Blocks of Causal Cognition

Theories of causal cognition describe how animals code cognitive primitives such as causal strength, directionality of relations, and other variables that allow inferences on the effect of interventions on causal links. We argue that these primitives and importantly causal generalization can be studied within an animal learning framework. Causal maps and other Bayesian approaches provide a normative framework for studying causal cognition, and associative theory provides algorithms for computing the acquisition of data-driven causal knowledge

Rats do learn XYX rules

The critical review of the rats learning pattern XYX and its transfer to novel stimuli is presented. Corballis claims that human infants and cotton top tamarins, if confronted with the same kind of task, may have used a subset of stimuli to solve the rule discrimination. Rats learning that XYX was the reinforced sequence may have matched the identity of the first and last stimulus (X), ignoring the interposed element (Y), and that this would be sufficient to discriminate XYX from YYX or YXX. Rats in each of the three groups were behaving on the basis of different learning strategies. Corballis challenges the lack of a statistical difference by way of a hypothesized floor effect. Configurable pattern-learning strategies are also ineffective in solving the discrimination. Mammals like rats can acquire rules that imply at least some level of abstraction and are considered to be involved in language learning have implications for any debate on the evolution of language and should be in accordance with an evolutionary perspective of cognition

Microcavity supported lipid membranes: versatile platforms for building asymmetric lipid bilayers and for protein recognition

Microcavity supported lipid bilayers (MSLB) are contact-free membranes suspended across aqueousfilled pores that maintain the lipid bilayer in a highly fluidic state and free from frictional interactions with substrate. Such platforms offer the prospect of liposome-like fluidity with the compositional versatility and addressability of supported lipid bilayers and thus offer significant opportunity for modelling membrane asymmetry, protein-membrane interactions and aggregation at the membrane interface. Herein, we evaluate their performance by studying the effect of transmembrane lipid asymmetry on lipid diffusivity, membrane viscosity and cholera toxin- ganglioside recognition across six symmetric and asymmetric membranes including binary compositions containing both fluid and gel phase, and ternary phase separated membrane compositions. Fluorescence lifetime correlation spectroscopy (FLCS) was used to determine the lateral mobility of lipid and protein, and electrochemical impedance spectroscopy (EIS) enabled detection of protein-membrane assembly over the nanomolar range. Transmembrane leaflet asymmetry was observed to have profound impact on membrane electrochemical resistance where the resistance of a ternary symmetric phase separated bilayer was found to be at least 2.6 times higher than the asymmetric bilayer with analogous composition at the distal leaflet but where the lower leaflet comprised only 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Similarly, the diffusion coefficient for MSLBs was observed to be 2.5 fold faster for asymmetric MSLBs where the lower leaflet is DOPC alone. Our results demonstrate that interplay of lipid packing across both membrane leaflets and concentration of GM1 both affect the extent of cholera toxin aggregation and consequent diffusion of the cholera-GM1 aggregates. Given that true biomembranes are both fluidic and asymmetric, MSLBs offer the opportunity for building greater biomimicry into biophysical models and the approach described demonstrates the value of MSLBs in studying aggregation and membrane associated multivalent interactions prevalent in many carbohydrates mediated processes

High-resolution saturation spectroscopy of singly-ionized iron with a pulsed uv laser

We describe the design and realization of a scheme for uv laser spectroscopy of singly-ionized iron (Fe II) with very high resolution. A buffer-gas cooled laser ablation source is used to provide a plasma close to room temperature with a high density of Fe II. We combine this with a scheme for pulsed-laser saturation spectroscopy to yield sub-Doppler resolution. In a demonstration experiment, we have examined an Fe II transition near 260 nm, attaining a linewidth of about 250 MHz. The method is well-suited to measuring transition frequencies and hyperfine structure. It could also be used to measure small isotope shifts in isotope-enriched samples.Comment: 9 pages, 5 figures, updated Fig. 3. For submission to J. Phys.

Manifestations of a spatial variation of fundamental constants on atomic clocks, Oklo, meteorites, and cosmological phenomena

The remarkable detection of a spatial variation in the fine-structure constant, alpha, from quasar absorption systems must be independently confirmed by complementary searches. In this letter, we discuss how terrestrial measurements of time-variation of the fundamental constants in the laboratory, meteorite data, and analysis of the Oklo nuclear reactor can be used to corroborate the spatial variation seen by astronomers. Furthermore, we show that spatial variation of the fundamental constants may be observable as spatial anisotropy in the cosmic microwave background, the accelerated expansion (dark energy), and large-scale structure of the Universe.Comment: 4 page

Tópicos de Geometria Plana Com o Software Geogebra: Proposta de sequências Didáticas

De acordo com a realidade das escolas em que trabalho, o ensino da geometria plana está deficitário, fazendo com que os alunos esqueçam com facilidade certas definições e propriedades. Um recurso que pode (e deve) ser usado é o que essa dissertação propõe: softwares educacionais para o estudo da geometria plana. Para ser mais objetiva é proposto o uso do software GeoGebra, que é gratuito, para mostrar alguns tópicos da geometria plana. A ideia é levar cada aluno a assimilação de definições e propriedades através de construções geométricas, usando-se o GeoGebra em sequências didáticas. Estas sequências didáticas poderão ser usadas inclusive em qualquer série do Ensino Médio, pois um dos objetivos do projeto é dar suporte para os alunos, independentemente da série que estão cursando. As primeiras sequências têm o objetivo de mostrar alguns recursos do software e as demais, construções geométricas e propriedades envolvidas

The biochemical, physiological, and metabolic effects of Apollo nominal mission and contingency diets on human subjects while on a simulated Apollo mission Final report, Feb. - Jun. 1966

Biochemical, physiological, and metabolic effects of simulated Apollo mission with space diet on human

Serial order of conditional stimuli as a discriminative cue for Pavlovian conditioning

The serial order in which events occur can be a signal for different outcomes and therefore might be a determinant of how an animal should respond. In this report, we propose a novel design for studying serial order learning in Pavlovian conditioning. In both Experiments 1a and 1b, hungry rats were trained with successively presented pairs of auditory and visual stimuli (e.g., A --> B) using four different stimuli (A-D). Four orders were paired with food (A --> B, B --> C, C --> D, D --> A) while the reversals were extinguished (B --> A, C --> B, D --> C, A --> D). An analysis of responding from the second element of each pair showed that the rats discriminated trial types that preceded food from those that did not. A replication of the effect using a completely counterbalanced design is described in Experiment 1b. These results suggest that rats can use the serial or temporal order of two sequentially presented non-overlapping elements as the basis for discrimination. Two associative accounts are suggested as possible mechanisms for solving the discrimination

Characterizing Cosmic-Ray Propagation in Massive Star-forming Regions: The Case of 30 Doradus and the Large Magellanic Cloud

Using infrared, radio, and γ-ray data, we investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using a phenomenological model based on the radio-far-infrared correlation within galaxies. Employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed γ-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and γ-ray data, we estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV)δ with δ ≈ 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV γ-ray data (δ ≈ 0.66 ± 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D_R ≈ (0.9-1.0) × 10^(27)(R/GV)0.7 cm^(2) s^(–1). We compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor