Internal Representations of Temporal Statistics and Feedback Calibrate Motor-Sensory Interval Timing

Humans have been shown to adapt to the temporal statistics of timing tasks so as to optimize the accuracy of their responses, in agreement with the predictions of Bayesian integration. This suggests that they build an internal representation of both the experimentally imposed distribution of time intervals (the prior) and of the error (the loss function). The responses of a Bayesian ideal observer depend crucially on these internal representations, which have only been previously studied for simple distributions. To study the nature of these representations we asked subjects to reproduce time intervals drawn from underlying temporal distributions of varying complexity, from uniform to highly skewed or bimodal while also varying the error mapping that determined the performance feedback. Interval reproduction times were affected by both the distribution and feedback, in good agreement with a performance-optimizing Bayesian observer and actor model. Bayesian model comparison highlighted that subjects were integrating the provided feedback and represented the experimental distribution with a smoothed approximation. A nonparametric reconstruction of the subjective priors from the data shows that they are generally in agreement with the true distributions up to third-order moments, but with systematically heavier tails. In particular, higher-order statistical features (kurtosis, multimodality) seem much harder to acquire. Our findings suggest that humans have only minor constraints on learning lower-order statistical properties of unimodal (including peaked and skewed) distributions of time intervals under the guidance of corrective feedback, and that their behavior is well explained by Bayesian decision theory.     

Molecular dynamics studies of the human CD4 protein

A dynamical model for an N-terminal fragment of the human CD4 protein has been determined by computer simulation. The protein has been studied both in vacuo and in solution. Data from both simulations agree moderately well with each other and with the crystal structure. All elements of secondary structure were retained during simulation. Point mutation and sequence replacement studies have shown that a loop in CD4, residues 40–52, is involved in binding with gp120, the human immunodeficiency virus surface glycoprotein.^1,2 Our results show that the gp120-binding loop and a few regions which bind to monoclonal antibodies and class II MHC molecules are the most highly motile areas of the protein. These results are consistent with the suggestion that CD4 binds to target molecules by using induced-fit contacts. © 1994 John Wiley & Sons, Inc.     

Resolution of genetic and uterine environmental effects in a family study of new dermatoglyphic measure: sole pattern ridge counts

The heritability of sole pattern ridge counts was examined in two family studies of endogamous castes from peninsular India. The phenotypes included ridge counts for each of the eight configurational areas separately, all areas combined, and only distal areas combined. Differences in heritability estimates were found between populations as well as among the individual configurational areas. Although some ridge counts do not show familial resemblance, others appear to be moderately heritable. Estimates of h2 range from 0.36 to 0.63 in one family series and from 0.22 to 0.51 in the other. In addition, significant uterine environmental effects were detected in one family series but not in the other.     

Topcats and underdogs: intraguild interactions among three apex carnivores across Asia's forestscapes

Intraguild interactions among carnivores have long held the fascination of ecologists. Ranging from competition to facilitation and coexistence, these interactions and their complex interplay influence everything from species persistence to ecosystem functioning. Yet, the patterns and pathways of such interactions are far from understood in tropical forest systems, particularly across countries in the Global South. Here, we examined the determinants and consequences of competitive interactions between dholes Cuon alpinus and the two large felids (leopards Panthera pardus and tigers Panthera tigris) with which they most commonly co-occur across Asia. Using a combination of traditional and novel data sources (N = 118), we integrate information from spatial, temporal, and dietary niche dimensions. These three species have faced catastrophic declines in their extent of co-occurrence over the past century; most of their source populations are now confined to Protected Areas. Analysis of dyadic interactions between species pairs showed a clear social hierarchy. Tigers were dominant over dholes, although pack strength in dholes helped ameliorate some of these effects; leopards were subordinate to dholes. Population-level spatio-temporal interactions assessed at 25 locations across Asia did not show a clear pattern of overlap or avoidance between species pairs. Diet-profile assessments indicated that wild ungulate biomass consumption by tigers was highest, while leopards consumed more primate and livestock prey as compared to their co-predators. In terms of prey offtake (ratio of wild prey biomass consumed to biomass available), the three species together harvested 0.4–30.2% of available prey, with the highest offtake recorded from the location where the carnivores reach very high densities. When re-examined in the context of prey availability and offtake, locations with low wild prey availability showed spatial avoidance and temporal overlap among the carnivore pairs, and locations with high wild prey availability showed spatial overlap and temporal segregation. Based on these observations, we make predictions for 40 Protected Areas in India where temporally synchronous estimates of predator and prey densities are available. We expect that low prey availability will lead to higher competition, and in extreme cases, to the complete exclusion of one or more species. In Protected Areas with high prey availability, we expect intraguild coexistence and conspecific competition among carnivores, with spill-over to forest-edge habitats and subsequent prey-switching to livestock. We stress that dhole–leopard–tiger co-occurrence across their range is facilitated through an intricate yet fragile balance between prey availability, and intraguild and conspecific competition. Data gaps and limitations notwithstanding, our study shows how insights from fundamental ecology can be of immense utility for applied aspects like large predator conservation and management of human–carnivore interactions. Our findings also highlight potential avenues for future research on tropical carnivores that can broaden current understanding of intraguild competition in forest systems of Asia and beyond.     

Changes in soluble amino nitrogen,protein, nitrate reductase activity and abscisic acid during development of wheat grain

Trends in the time course, changes in the moisture, soluble amino acids, proline, abscisic acid contents and nitrate reductase activity determined byin vivo method in the developing seeds of wheat were studied. Maximum dry matter augmentation in the seed took place in the period between 10–30 days after anthesis. Per cent moisture and moisture content started declining 15 days and 25 days after anthesis, respectively. Levels of soluble amino acids, proline and nitrate reductase activity were higher during initial stages of seed development, but decreased with increasing magnitude of dehydration and accumulation of abscisic acid (ABA) in the maturing seeds.     

An essential histidine residue in the catalytic mechanism of mammalian glutathione reductase

Glutathione reductase from human erythrocytes was inactivated by ethoxyformic anhydride, and > 95% activity was lost by modification of about 1–1.5 histidine residues per flavin (or subunit), as measured by the increased absorbance at 240 nm. Full reactivation was obtained with hydroxylamine. The rate of inactivation increased with pH and an apparent pK = 5.9 was obtained for the protolytic dissociation. The modified enzyme was inactive with NADPH and GSSG as substrates, but almost fully active in catalysis of a transhydrogenase reaction involving pyridine nucleotides. The visible absorption spectrum of oxidized or two-electron-reduced enzyme was not changed, but the flavin fluorescence of oxidized enzyme increased 2-fold after the modification. NADPH or NADP⁺ did not protect the enzyme against inactivation. It is concluded that the modification affects a histidine involved in the second half-reaction of the catalysis, i.e. reduction of GSSG by the dithiol of reduced enzyme. Glutathione reductase from three additional mammalian sources was similarly inactivated, but enzyme from yeast was much less inactivated by the corresponding treatment with ethoxyformic anhydride.     

Purification,Characterization and Antibacterial Properties of Peptide from Marine Ascidian Didemnum sp.

International Journal of Peptide Research and Therapeutics - Marine ecosystems are unique and a largely diverse chest of natural resources which are still to be explored for new marine species....     

Evaluation of photosynthetic efficiency of yam bean (Pachyrhizus erosus L.) at saturating photon flux density under elevated carbon dioxide

Physiology and Molecular Biology of Plants - The future CO2 concentration is projected to reach 900–1000 ppm levels by the end of twenty-first century, pertaining to global climatic...