Geometrical computations explain projection patterns of long-range horizontal connections in visual cortex

Neurons in primary visual cortex respond selectively to oriented stimuli such as edges and lines. The long-range horizontal connections between them are thought to facilitate contour integration. While many physiological and psychophysical findings suggest that collinear or association field models of good continuation dictate particular projection patterns of horizontal connections to guide this integration process, significant evidence of interactions inconsistent with these hypotheses is accumulating. We first show that natural random variations around the collinear and association field models cannot account for these inconsistencies, a fact that motivates the search for more principled explanations. We then develop a model of long-range projection fields that formalizes good continuation based on differential geometry. The analysis implicates curvature(s) in a fundamental way, and the resulting model explains both consistent data and apparent outliers. It quantitatively predicts the (typically ignored) spread in projection distribution, its nonmonotonic variance, and the differences found among individual neurons. Surprisingly, and for the first time, this model also indicates that texture (and shading) continuation can serve as alternative and complementary functional explanations to contour integration. Because current anatomical data support both (curve and texture) integration models equally and because both are important computationally, new testable predictions are derived to allow their differentiation and identification.     

First Principles Investigation of Cold Curves of Metals

The rapid development of better high pressure experimental techniques combined with efficient and accurate density functional calculations of the structural properties of materials provide a new avenue to promote the study of materials at high pressures, which is currently based mostly on simple phenomenological modelling. The progress of experimental results into higher-pressure regimes represents a challenge to the phenomenological approaches, which can be addressed by carefully considered ab initio calculations. We present cold curves of several elements, calculated using different approximations of DFT and compare them with available experimental data. The comparison shows good agreement both in simple single phase and complex multi-phase cases. It suggests that DFT may be used to extrapolate high pressure behaviour of materials beyond the currently possible pressure range, with a robust estimate of the accuracy of the extrapolation based on various DFT implementations.     

User attitudes towards news content personalization

Personalizing news content requires to choose the appropriate depth of personalization and to assess the extent to which readers’ explicit expressions of interest in general and specific news topics can be used as the basis for personalization. A preliminary survey examined 117 respondents’ attitudes towards news content personalization and their interest in various news topics and subtopics. The second survey examined 23 participants’ declared and actual interests. Participants preferred personalization based on general news topics. Declared interest in general news topics adequately predicted the actual interests in some topics, while in others users’ interests differed between general news topics and subtopics. The variance in interest in items also differed among topics. Thus, different personalization methods should be used for different topics. For some, such as ‘Sports’, users show either high interest or no interest at all. In the latter case most articles related to the topic should be removed, with the exception of items that refer to unique events that may raise general interest according to the expressed interest. In other topics, such as ‘Science & Technology’, most users are interested in important articles, even if they are not interested in the general news topic. Here, the filtering technique should identify the important articles and present them to all readers. The results can be used to develop effective and simple personalization mechanisms which can be applied to the personalization of news, as well as to other domains.     

LIQUID-LIQUID EXTRACTION OF METAL IONS BY NEUTRAL PHOSPHOR- AMIDES. PART I,EXTRACTION OF URANYL IONS FROM NITRATE AND SULPHATE MEDIA. EXAMINATION OF EXTRACTED SPECIES BY UV/V1S AND sip NMR SPECTROSCOPY.

ABSTRACT

The extraction of uranyl nitrate and uranyl sulphate from aqueous media by the neutral chelating diphosphoramides CH₃-N[P(OKNMe₂)₂] (NIPA) and its less hydrophilic homologues R-N[P(O)(NMe₂)₂]₂ (R = -C₁₂H₂₅ (OD1PA) or -C₁₆H₃₃ (OHDIPA)), diluted in CH₃NO₂ or toluene, has been studied. In the presei ce of HNO₃, NaNO₃, NaCl, and Na₂SO₄ as salting-out agents, extraction is generally excellent. Some of the extracted complex species have been identified by comparing their ³¹P NMR and UV/vis spectra with those of pure complexes of known structure. The results are compared with extractions using tri-n-butyl phosphate (TBP) as complexing agent.     

Efficient Detection of Vacuity in Temporal Model Checking

The ability to generate a counter-example is an important feature of model checking tools, because a counter-example provides information to the user in the case that the formula being checked is found to be non-valid. In this paper, we turn our attention to providing similar feedback to the user in the case that the formula is found to be valid, because valid formulas can hide real problems in the model. For instance, propositional logic formulas containing implications can suffer from antecedent failure, in which the formula is trivially valid because the pre-condition of the implication is not satisfiable. We call this vacuity, and extend the definition to cover other kinds of trivial validity. For non-vacuously valid formulas, we define an interesting witness as a non-trivial example of the validity of the formula. We formalize the notions of vacuity and interesting witness, and show how to detect vacuity and generate interesting witnesses in temporal model checking. Finally, we provide a practical solution for a useful subset of ACTL formulas.     

Adaptive Application of SAT Solving Techniques

New heuristics and strategies have enabled major advancements in SAT solving in recent years. However, experimentation has shown that there is no winning solution that works in all cases. A degradation of orders of magnitude can be observed if the wrong heuristic is chosen. The problem is that it is impossible to know, in advance, which heuristics are best for a given problem. Consequently, many ideas - those that turn out to be useful for a small subset of the cases, but significantly increase run times on most others - are discarded.We propose the notion of Adaptive Solving as a possible solution to this problem. In our framework, the SAT solver monitors the effectiveness of the search on-the-fly using a Performance Metric. The metric gives a score according to its assessment of the search progress. Based on this score, one or more heuristics are turned on or off. The goal is to use a specific heuristic or strategy when it is advantageous, and turn it off when it is not, before it does too much damage. We suggest several possible metrics, and compare their effectiveness. Our adaptive solver achieves significant speedups on a large set of examples. We also show that applying different heuristics on different parts of the search space can improve run times even beyond what can be achieved by the best heuristic on its own.     

Work measurement for estimating food preparation time of a bioregenerative diet

During space missions, such as the prospective Mars mission, crew labor time is a strictly limited resource. The diet for such a mission (based on crops grown in a bioregenerative life support system) will require astronauts to prepare their meals essentially from raw ingredients. Time spent on food processing and preparation is time lost for other purposes. Recipe design and diet planning for a space mission should therefore incorporate the time required to prepare the recipes as a critical factor. In this study, videotape analysis of an experienced chef was used to develop a database of recipe preparation time. The measurements were highly consistent among different measurement teams. Data analysis revealed a wide variation between the active times of different recipes, underscoring the need for optimization of diet planning. Potential uses of the database developed in this study are discussed and illustrated in this work.     

Learning and generalization with the information bottleneck

The Information Bottleneck is an information theoretic framework that finds concise representations for an ‘input’ random variable that are as relevant as possible for an ‘output’ random variable. This framework has been used successfully in various supervised and unsupervised applications. However, its learning theoretic properties and justification remained unclear as it differs from standard learning models in several crucial aspects, primarily its explicit reliance on the joint input–output distribution. In practice, an empirical plug-in estimate of the underlying distribution has been used, so far without any finite sample performance guarantees. In this paper we present several formal results that address these difficulties. We prove several finite sample bounds, which show that the information bottleneck can provide concise representations with good generalization, based on smaller sample sizes than needed to estimate the underlying distribution. The bounds are non-uniform and adaptive to the complexity of the specific model chosen. Based on these results, we also present a preliminary analysis on the possibility of analyzing the information bottleneck method as a learning algorithm in the familiar performance-complexity tradeoff framework. In addition, we formally describe the connection between the information bottleneck and minimal sufficient statistics.     

Unsupervised natural image patch learning

Computational Visual Media - A metric for natural image patches is an important tool for analyzing images. An efficient means of learning one is to train a deep network to map an image patch to a...     

Nectar Minerals as Regulators of Flower Visitation in Stingless Bees and Nectar Hoarding Wasps

Various nectar components have a repellent effect on flower visitors, and their adaptive advantages for the plant are not well understood. Persea americana (avocado) is an example of a plant that secretes nectar with repellent components. It was demonstrated that the mineral constituents of this nectar, mainly potassium and phosphate, are concentrated enough to repel honey bees, Apis mellifera, a pollinator often used for commercial avocado pollination. Honey bees, however, are not the natural pollinator of P. americana, a plant native to Central America. In order to understand the role of nectar minerals in plant—pollinator relationships, it is important to focus on the plant’s interactions with its natural pollinators. Two species of stingless bees and one species of social wasp, all native to the Yucatan Peninsula, Mexico, part of the natural range of P. americana, were tested for their sensitivity to sugar solutions enriched with potassium and phosphate, and compared with the sensitivity of honey bees. In choice tests between control and mineral-enriched solutions, all three native species were indifferent for mineral concentrations lower than those naturally occurring in P. americana nectar. Repellence was expressed at concentrations near or exceeding natural concentrations. The threshold point at which native pollinators showed repellence to increasing levels of minerals was higher than that detected for honey bees. The results do not support the hypothesis that high mineral content is attractive for native Hymenopteran pollinators; nevertheless, nectar mineral composition may still have a role in regulating flower visitors through different levels of repellency.