scholarly journals A Critical Look at Linus Pauling’s Influence on the Understanding of Chemical Bonding

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4695
Author(s):  
Sudip Pan ◽  
Gernot Frenking
Keyword(s):  
Chemical Bonding ◽  
Close Association ◽  
Valence Bond ◽  
Theoretical Description ◽  
Binding Model ◽  
Linus Pauling ◽  
Bonding Theory ◽  
Pair Bonds ◽  
Wide Range ◽  
Further Development

The influence of Linus Pauling on the understanding of chemical bonding is critically examined. Pauling deserves credit for presenting a connection between the quantum theoretical description of chemical bonding and Gilbert Lewis’s classical bonding model of localized electron pair bonds for a wide range of chemistry. Using the concept of resonance that he introduced, he was able to present a consistent description of chemical bonding for molecules, metals, and ionic crystals which was used by many chemists and subsequently found its way into chemistry textbooks. However, his one-sided restriction to the valence bond method and his rejection of the molecular orbital approach hindered further development of chemical bonding theory for a while and his close association of the heuristic Lewis binding model with the quantum chemical VB approach led to misleading ideas until today.

Application of TEM to Deformation, Wear, and Fracture of Ceramics

1974 ◽  
Vol 32 ◽  
pp. 472-473
Author(s):  
B. J. Hockey
Keyword(s):  
Wear Resistance ◽  
High Temperature ◽  
Mechanical Behavior ◽  
Brittle Materials ◽  
High Temperature Strength ◽  
Wide Range ◽  
Corrosive Environments ◽  
Further Development

Ceramics, such as Al2O3 and SiC have numerous current and potential uses in applications where high temperature strength, hardness, and wear resistance are required often in corrosive environments. These materials are, however, highly anisotropic and brittle, so that their mechanical behavior is often unpredictable. The further development of these materials will require a better understanding of the basic mechanisms controlling deformation, wear, and fracture.The purpose of this talk is to describe applications of TEM to the study of the deformation, wear, and fracture of Al2O3. Similar studies are currently being conducted on SiC and the techniques involved should be applicable to a wide range of hard, brittle materials.

QCD at Fixed Order: Processes

2018 ◽  
Author(s):  
John Campbell ◽  
Joey Huston ◽  
Frank Krauss
Keyword(s):  
Hadron Collider ◽  
Detailed Comparison ◽  
Theoretical Description ◽  
Higgs Bosons ◽  
Final States ◽  
Collider Physics ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Fixed Order ◽  
The Subject

At the core of any theoretical description of hadron collider physics is a fixed-order perturbative treatment of a hard scattering process. This chapter is devoted to a survey of fixed-order predictions for a wide range of Standard Model processes. These range from high cross-section processes such as jet production to much more elusive reactions, such as the production of Higgs bosons. Process by process, these sections illustrate how the techniques developed in Chapter 3 are applied to more complex final states and provide a summary of the fixed-order state-of-the-art. In each case, key theoretical predictions and ideas are identified that will be the subject of a detailed comparison with data in Chapters 8 and 9.

scholarly journals β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 5. Adsorption Isotherm and Equation of State Revisited, Impact of pH

2021 ◽  
Vol 5 (1) ◽  
pp. 14
Author(s):  
Georgi G. Gochev ◽  
Volodymyr I. Kovalchuk ◽  
Eugene V. Aksenenko ◽  
Valentin B. Fainerman ◽  
Reinhard Miller
Keyword(s):  
Theoretical Description ◽  
Fluid Interfaces ◽  
Interfacial Behavior ◽  
Current State ◽  
Air Interface ◽  
Direct Measurements ◽  
Wide Range ◽  
Dilational Viscoelasticity ◽  
Parameter Values ◽  
Β Lactoglobulin

The theoretical description of the adsorption of proteins at liquid/fluid interfaces suffers from the inapplicability of classical formalisms, which soundly calls for the development of more complicated adsorption models. A Frumkin-type thermodynamic 2-d solution model that accounts for nonidealities of interface enthalpy and entropy was proposed about two decades ago and has been continuously developed in the course of comparisons with experimental data. In a previous paper we investigated the adsorption of the globular protein β-lactoglobulin at the water/air interface and used such a model to analyze the experimental isotherms of the surface pressure, Π(c), and the frequency-, f-, dependent surface dilational viscoelasticity modulus, E(c)f, in a wide range of protein concentrations, c, and at pH 7. However, the best fit between theory and experiment proposed in that paper appeared incompatible with new data on the surface excess, Γ, obtained from direct measurements with neutron reflectometry. Therefore, in this work, the same model is simultaneously applied to a larger set of experimental dependences, e.g., Π(c), Γ(c), E(Π)f, etc., with E-values measured strictly in the linear viscoelasticity regime. Despite this ambitious complication, a best global fit was elaborated using a single set of parameter values, which well describes all experimental dependencies, thus corroborating the validity of the chosen thermodynamic model. Furthermore, we applied the model in the same manner to experimental results obtained at pH 3 and pH 5 in order to explain the well-pronounced effect of pH on the interfacial behavior of β-lactoglobulin. The results revealed that the propensity of β-lactoglobulin globules to unfold upon adsorption and stretch at the interface decreases in the order pH 3 > pH 7 > pH 5, i.e., with decreasing protein net charge. Finally, we discuss advantages and limitations in the current state of the model.

scholarly journals Topology of the Electron Density and of Its Laplacian from Periodic LCAO Calculations on f-Electron Materials: The Case of Cesium Uranyl Chloride

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4227
Author(s):  
Alessandro Cossard ◽  
Silvia Casassa ◽  
Carlo Gatti ◽  
Jacques K. Desmarais ◽  
Alessandro Erba
Keyword(s):  
Electron Density ◽  
Chemical Bonding ◽  
Topological Analysis ◽  
Theoretical Description ◽  
Basis Functions ◽  
Quantum Mechanical ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Orbitals ◽  
Uranyl Chloride

The chemistry of f-electrons in lanthanide and actinide materials is yet to be fully rationalized. Quantum-mechanical simulations can provide useful complementary insight to that obtained from experiments. The quantum theory of atoms in molecules and crystals (QTAIMAC), through thorough topological analysis of the electron density (often complemented by that of its Laplacian) constitutes a general and robust theoretical framework to analyze chemical bonding features from a computed wave function. Here, we present the extension of the Topond module (previously limited to work in terms of s-, p- and d-type basis functions only) of the Crystal program to f- and g-type basis functions within the linear combination of atomic orbitals (LCAO) approach. This allows for an effective QTAIMAC analysis of chemical bonding of lanthanide and actinide materials. The new implemented algorithms are applied to the analysis of the spatial distribution of the electron density and its Laplacian of the cesium uranyl chloride, Cs2UO2Cl4, crystal. Discrepancies between the present theoretical description of chemical bonding and that obtained from a previously reconstructed electron density by experimental X-ray diffraction are illustrated and discussed.

The functions and positions of political parties in consociational democracies: theoretical and empirical contexts

2020 ◽  
pp. 28-33
Author(s):  
O. Morhuniuk
Keyword(s):  
Political Parties ◽  
The Netherlands ◽  
Party System ◽  
Party Competition ◽  
European Countries ◽  
The Past ◽  
Democratic Regimes ◽  
Wide Range ◽  
Key Aspects ◽  
Further Development

An article is devoted to the analysis of the functions and formats of political parties in consociational democracies. In particular, it is defined that parties that represent the interests of certain subcultures in society and that reach a consensus among themselves at the level of political agreements are called segmental. At the same time, parties that encapsulate different subgroups of the society that cooperate inside the party within main features of the consociational theory (grand coalition, mutual veto, proportionality in representations, and independence of segments or society subcultures) are called consociational. The theory of consociationalism has received a wide range of theoretical additions and criticism from political scientists over the past fifty years. And while political parties should have been, by definition, one of the key aspects of research within such democratic regimes (parties are part of large coalitions and agents of representation of certain subcultures), there is very scarce number of literature that focuses on this aspect. Therefore, the presented article provides a description of the functions of political parties that could be observed as inside their subcultures as well as in interaction with other segmental parties. Based on the experience of two European countries in the period of “classical” consociationalism (Belgium and the Netherlands), we explain the functions of the parties we have defined in such societies with examples of relevant consociational practices in them. Simultaneously with the analysis of segmental parties, the article also offers the characteristics of consociational parties. The emergence of such parties has its own institutional and historical features. The way of further development of the party system and the level of preservation of consociational practices makes it possible to understand the nature of changes in the societies. Similarly, the analysis of the forms of party competition and interaction between segmental parties makes it possible to outline the forms of those consociational changes that are taking place in the research countries.

scholarly journals Tunable aziridinium ylide reactivity: non-covalent interactions enable divergent product outcomes

2021 ◽  
Author(s):  
Kate Nicastri ◽  
Soren Zappia ◽  
Jared Pratt ◽  
Julia Duncan ◽  
Ilia Guzei ◽  
...  
Keyword(s):  
Chemical Space ◽  
Steric Effects ◽  
Computational Studies ◽  
Rapid Preparation ◽  
Rotational Barriers ◽  
Wide Range ◽  
Non Covalent Interactions ◽  
Further Development ◽  
Covalent Interactions

Methods for rapid preparation of densely functionalized and stereochemically complex N-heterocyclic scaffolds are in demand for exploring potential new bioactive chemical space. This work describes experimental and computational studies to better understand the features of aziridinium ylides as intermediates for the synthesis of highly substituted dehydromorpholines. The development of this chemistry has enabled the extension of aziridinium ylide chemistry to the concomitant formation of both a C–N and a C–O bond in a manner that preserves the stereochemical information embedded in the substrate. The chemistry is tolerant of a wide range of functionalities that can be employed for DNA-encoded library (DEL) synthesis to prepare diverse libraries of heterocycles with potential bioactivity. In addition, we have uncovered several key insights that describe the importance of steric effects, rotational barriers around the C–N bond of the aziridinium ylide, and non-covalent interactions (NCIs) on the ultimate reaction outcome. These critical insights will assist in the further development of this chemistry to generate novel and complex N-heterocycles that will further expand complex amine chemical space.

RELATIONSHIPS BETWEEN ATTACK RATES AND SURVIVAL OF WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE), AND BUD DEVELOPMENT OF DOUGLAS-FIR, PSEUDOTSUGA MENZIESII (MIRB.) FRANCO

1992 ◽  
Vol 124 (2) ◽  
pp. 347-358 ◽  
Author(s):  
Roy F. Shepherd
Keyword(s):  
Close Association ◽  
Spruce Budworm ◽  
Larval Survival ◽  
Douglas Fir ◽  
Choristoneura Occidentalis ◽  
Western Spruce Budworm ◽  
Bud Development ◽  
Feeding Sites ◽  
Vegetative Buds ◽  
Wide Range

AbstractIndividual larvae of western spruce budworm (Choristoneura occidentalis Freeman) were observed from overwintering emergence to pupation at six locations spread over a wide range of altitudes and thus climate. A weekly census of 100 lower-crown buds per plot indicated large differences in rates of bud development and larval survival among locations.Emerging second-instar larvae attempted to mine swelling buds of Douglas-fir. If the buds were hard and tight, larvae mined 1-year-old needles until penetrable buds were available. Larvae dispersed over the crowns with only one larva becoming established in each bud; thus, many early-emerging and surplus larvae could not find suitable feeding sites and disappeared. Within the protective bud, survival was high. After buds flushed and larvae became exposed, densities dropped, probably due to increased predation and decreased food quality. Correlations indicated a close association between larval survival for the exposed period between bud flush and pupation, and overall larval survival.Douglas-fir trees responded to initial bud removal, but not to needle removal, by inducing latent buds in the axils of needles to grow into active vegetative buds ready to develop and flush the next spring. The number of these new vegetative buds formed was greatest when the initial buds were removed early in the season before flush, and decreased thereafter. Trees with vigorous crowns had the greatest response to defoliation by inducing the largest number of latent buds into becoming active vegetative buds; these were found mainly on the 2- and 3-year-old internodes.

scholarly journals FORMATION OF APPROACHES TO INTERNATIONAL COOPERATION IN THE FIELD OF HIGHER EDUCATION

2019 ◽  
Vol 7 (6) ◽  
pp. 727-731
Author(s):  
Margarita Anatolyevna Ganyushina ◽  
Svetlana Nikolaevna Kurbakova ◽  
Elena Grigorievna Galizina ◽  
Victoria Valerievna Lopatinskaya ◽  
Natalya Yevgenievna Ryazanova
Keyword(s):  
Higher Education ◽  
International Cooperation ◽  
Formal Education ◽  
Educational Process ◽  
Point Of View ◽  
Educational Opportunities ◽  
Wide Range ◽  
The Future ◽  
Further Development ◽  
Important Basis

Purpose of the study: The paper is devoted to the formation of approaches to international cooperation in the field of higher education. Main Findings: It has been established that in the future, there is a need for broad initiatives from all countries for the qualitative improvement of higher education. It has been determined that the most important basis for the future prosperity of the world economy and society is a strong and diverse training of young people. Applications of this study: From the point of view of further development of new educational information means, the importance of non-formal education integrated into the educational process will grow. The originality of this study: It has been proved that self-education will play an increasing role. In the field of higher education, the cooperation between different partners and a wide range of different educational opportunities will be developed in order to give everyone the opportunity to improve their knowledge, both in the personal and professional sphere.

Implementation of the principles, standards and rules of international customs law: individual and overall levels

2021 ◽  
pp. 102-111
Author(s):  
Serhii Perepolkin
Keyword(s):  
International Law ◽  
Practical Significance ◽  
Clear Understanding ◽  
The European Union ◽  
Public Authorities ◽  
Customs Unions ◽  
Wide Range ◽  
And Control ◽  
Further Development

Purpose. The purpose of the study is to submit to the discussion of domestic international lawyers a proposal to introduce the use in scientific and educational works of the classification of the implementation of the principles, norms and standards of international customs law into two types: individual and overall. Methodology. In order to achieve the goal of the study, have been analyzed scientific approaches to understand the implementation of international law and the classification of its types. In article have been studied an Implementation articles developed under the auspices of the Customs Agreements Cooperation Council; recommendations and resolutions, conventions of the Member States of the European Union, current international agreements and other acts of Ukrainian legislation on customs matters. Results. In the article it was substantiated that individual implementation along with the states can be carried out also by separate customs territories which have full autonomy in the realization of foreign trade; customs unions; economic unions; international organizations and other participants in international customs relations. The joint implementation of the principles, norms, and standards of international customs law is carried out by two or more of its subjects simultaneously. To achieve this goal, the subjects of international customs law can use a wide range of law-making, organizational, coordination, information and control tools. Scientific novelty. It was proved that the classification of the implementation of principles, norms, and standards of international customs law into individual and overral, in contrast to its differentiation into domestic and international, most accurately reflects all types of subjects of international customs law capable of participating in such activities. Practical significance. The introduction of the classification of the implementation of principles, norms, and standards into individual and joint, will contribute to the further development of research in this area, as well as the development of a clear understanding of the implementation of officials of public authorities of Ukraine.

Introduction

1992 ◽  
Author(s):  
John A. Tossell ◽  
David J. Vaughan
Keyword(s):  
Crystal Structures ◽  
Chemical Bonding ◽  
Alkali Halides ◽  
Ionic Character ◽  
Ionic Radii ◽  
Ionic Model ◽  
Coordination Numbers ◽  
Bonding Theory ◽  
Distribution Of Elements ◽  
Complex Crystal

The early descriptions of chemical bonding in minerals and geological materials utilized purely ionic models. Crystals were regarded as being made up of charged atoms or ions that could be represented by spheres of a particular radius. Based on interatomic distances obtained from the early work on crystal structures, ionic radii were calculated for the alkali halides (Wasastjerna, 1923) and then for many elements of geochemical interest by Goldschmidt (1926). Modifications to these radius values by Pauling (1927), and others took account of such factors as different coordination numbers and their effects on radii. The widespread adoption of ionic models by geochemists resulted both from the simplicity and ease of application of these models and from the success of rules based upon them. Pauling’s rules (1929) enabled the complex crystal structures of mineral groups such as the silicates to be understood and to a limited extent be predicted; Goldschmidt’s rules (1937) to some degree enabled the distribution of elements between mineral phases or mineral and melt to be understood and predicted. Such rules are further discussed in later chapters. Ionic approaches have also been used more recently in attempts to simulate the structures of complex solids, a topic discussed in detail in Chapter 3. Chemical bonding theory has, of course, been an important component of geochemistry and mineralogy since their inception. Any field with a base of experimental data as broad as that of mineralogy is critically dependent upon theory to give order to the data and to suggest priorities for the accumulation of new data. Just as the bond with predominantly ionic character was the first to be quantitatively understood within solidstate science, the ionic bonding model was the first used to interpret mineral properties. Indeed, modern studies described herein indicate that structural and energetic properties of some minerals may be adequately understood using this model. However, there are numerous indications that an ionic model is inadequate to explain many mineral properties. It also appears that some properties that may be rationalized within an ionic model may also be rationalized assuming other limiting bond types.

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