Search results for "Polar"

Spatial distribution of two maternal messengers encoding two sea urchin cell surface proteins

1993

We have localized, byin situ hybridization, two messengers, called bepl and bep4 (butanol extracted proteins), coding for cell surface proteins, involved in cell interaction, in sections of eggs of the sea urchinP. lividus. These maternal RNAs are spatially distributed in a gradient with a maximum at one pole of the egg. These results represent the first demonstration of the existence of a gradient of informational molecules in the sea urchin egg,i.e., the biological material for which the gradient theory was first proposed.

Functional fixedness and functional reduction as common sense reasonings in chemical equilibrium and in geometry and polarity of molecules

2000

Many of the learning difficulties in the specific domain of chemistry are found not only in the ideas already possessed by students but in the strategic and procedural knowledge that is characteristic of everyday thinking. These defects in procedural knowledge have been described as functional fixedness and functional reduction. This article assesses the procedural difficulties of students (grade 12 and first and third year of university) based on common sense reasoning in two areas of chemistry: chemical equilibrium and geometry and polarity of molecules. In the first area, the theme of external factors affecting equilibria (temperature and concentration change) was selected because the ex…

Stabilization of polar solid oxide surfaces: competition between adsorption and reconstruction

2002

Multi-cationic spinel compounds are solids that exhibit polar faces. X-ray Photoelectron spectroscopy revealed the main phenomena allowing the stabilization of these faces, carried out as a function of the material treatment, particularly the cooling rate after thermal treatment at a high temperature (1200°C). This study showed that, whatever the cooling rate, each sample is subject to a significant hydroxylation that reduces the polarity. Nevertheless, it appears that the hydroxyl group content at the surface is a strong function of the cooling rate. Indeed, whereas quenched materials are subject to high levels of hydroxylation, slowly cooled samples are sparingly hydroxylated. This phenom…

Overview of the Evalita 2014 SENTIment POLarity Classification Task

2014

International audience; English. The SENTIment POLarity Classification Task (SENTIPOLC), a new shared task in the Evalita evaluation campaign , focused on sentiment classification at the message level on Italian tweets. It included three subtasks: subjectivity classification, polarity classification, and irony detection. SENTIPOLC was the most participated Evalita task with a total of 35 submitted runs from 11 different teams. We present the datasets and the evaluation methodology, and discuss results and participating systems. Italiano. Descriviamo modalit a e risultati della campagna di valutazione di sistemi di sentiment analysis (SENTIment POLarity Classification Task), proposta per la …

When Predicates Behave Badly

2021

The main topics of this chapter are two: a discussion (at times very critical) of certain themes in Bolzano’s, Frege’s, and Wittgenstein’s work, and an analysis of some propositional attitudes. A new polarity correct–incorrect, distinct both from true–false, and from grammatical–ungrammatical, also begins to emerge.

Structural Approaches to Explain the Selectivity of COX-2 Inhibitors: Is There a Common Pharmacophore?

2000

The identification and characterisation of the isoenzyme cyclooxygenase 2 (COX-2) stimulated investigations to develop efficient non-steroidal anti-inflammatory drugs with reduced side effects compared to standard NSAIDs. This review will focus on the structural features needed to achieve COX-2 selectivity. Five structural classes can be identified together with a class bearing little or no resemblance to one another in their molecular structure. The most interesting point is the very distinct structure/activity relationship. On the one hand only minor modifications to a particular compound induce a drastic change in its COX selectivity and on the other hand the structural prerequisites in …

An Interlude: Matters of Method

2021

The discussion of everyday discourse developed so far makes two entirely new problems inescapable. The first is that in everyday discourse there is no algebra, either Boolean or non-Boolean, of truth values. The second is that a new polarity (conceptually) correct–incorrect, distinct both from true–false, and from grammatical–ungrammatical, becomes indispensable.

Dynamic electric field assisted multi-dimensional liquid chromatography of biological samples

2005

Complex biological samples require very high resolution separation strategies. The platform introduced here capitalises on the hyphenation of liquid chromatographic (LC) and electric potential gradient electrochromatographic multi-dimensional separation genres. First-dimension selectivity is provided by simultaneous size exclusion (SEC) and strong cation exchange (SCX) chromatography modes, while the second dimension comprises reversed phase (RP) characteristics in a dynamic (time-variant) electric field. The time-variant potential gradient with reversal of polarity is applied across the second dimension monolithic capillary throughout the duration of the solvent strength gradient elution. …

Subduction Polarity Reversal Triggered by Oceanic Plateau Accretion: Implications for Induced Subduction Initiation

2021

Drawback of ICA Procedure on EEG: Polarity Indeterminacy at Local Optimization

2008

Independent component analysis (ICA) has been extensively applied to reject artifacts in electroencephalography (EEG) signal processing. The first step is to extract the independent component activations from the electrode records, and then project the desired components back to the electrodes. After the composition of the projected component is analyzed in details under ICA procedure, this study shows that since ICA may extract some source components at the local optimization in high-dimensional EEG signal space, the artificial polarity indeterminacy may happen on the projected component at some electrodes. By numerical simulations, this issue also exhibits that this polarity ambiguity occ…