Search results for "Polarity"
showing 10 items of 196 documents
Quantitative characterization of the global electrophilicity power of common diene/dienophile pairs in Diels–Alder reactions
2002
Abstract The global electrophilicity power, ω, of a series of dienes and dienophiles commonly used in Diels–Alder reactions may be conveniently classified within a unique relative scale. Useful information about the polarity of transition state structures expected for a given reaction may be obtained from the difference in the global electrophilicity power, Δω, of the diene/dienophile interacting pair. Thus the polarity of the process can be related with non-polar (Δω small, pericyclic processes) and polar (Δω big, ionic processes) mechanisms.
Characterization of PTW-31015 PinPoint ionization chambers in photon and proton beams
2018
The increased use of complex forms of radiotherapy using small-field photon and proton beams has invoked a growing interest in the use of micro-ionization chambers. In this study, 48 PTW-TM31015 PinPoint-type micro-ionization chambers that are used in the commissioning and patient specific QA of a proton pencil beam scanning (PBS) delivery system have been characterized in proton and high-energy photon beams. In both beam modalities, the entire set of PinPoint chambers was characterized by imaging them, by evaluating their stability using check source measurements, by experimentally determining the ion recombination, polarity effect and by cross calibrating them in terms of absorbed dose to…
Moving Magnetic Features around a Pore
2017
A. J. Kaithakkal et. al.
Polarity and bioelectrical patterning in a linear chain of non-excitable cells
2020
Abstract Polarity in multicellular systems is influenced by bioelectrical signals because electric potentials can act as spatio-temporal patterns for other biochemical processes that eventually emerge as long-lasting biological outcomes. We study the role of the electric potential in establishing head-tail polarity for the case of a chain of non-excitable cells. This biophysical model incorporates both single-cell (membrane ion channels) and multicellular (intercellular gap junctions) characteristics. The results are presented in the form of a bioelectrical phase space that complements traditional biochemical approaches and provides qualitative insights for the case of anterior/posterior po…
Purely long-range polar molecules composed of identical lanthanide atoms
2019
International audience; Doubly polar molecules, possessing an electric dipole moment and a magnetic dipole moment, can strongly couple to both an external electric field and a magnetic field, providing unique opportunities to exert full control of the system quantum state at ultracold temperatures. We propose a method for creating a purely long-range doubly polar homonuclear molecule from a pair of strongly magnetic lanthanide atoms, one atom being in its ground level and the other in a superposition of quasi-degenerate opposite-parity excited levels [Phys. Rev. Lett. 121, 063201 (2018)]. The electric dipole moment is induced by coupling the excited levels with an external electric field. W…
Gas—liquid chromatographic analyses
1989
Abstract The retention (I), dispersion (IM) and selectivity (I*) indices of sixteen polychlorinated dibenzo-p-dioxins and fourteen polychlorinated dibenzofurans were determined on a low-polarity HP-5 capillary column using a gas chromatograph connected with an ion-selective detector. IM and I* values were also calculated for all 73 dibenzo-p-dioxins from the di- to the octachloro isomer and for all possible 135 chlorinated dibenzofurans based on the predicted retention index data reported earlier. The effect of the position of chlorination is shown and the results are compared with those for several series of chlorinated aromatics.
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 …