1,107 research outputs found
Low-frequency linear vibrations of single-walled carbon nanotubes: Analytical and numerical models
No full textLow-frequency vibrations of single-walled carbon nanotubes with various boundary conditions are considered in the framework of the Sanders–Koiter thin shell theory. Two methods of analysis are proposed. The first approach is based on the Rayleigh–Ritz method, a double series expansion in terms of Chebyshev polynomials and harmonic functions is considered for the displacement fields; free and clamped edges are analysed. This approach is partially numerical. The second approach is based on the same thin shell theory, but the goal is to obtain an analytical solution useful for future developments in nonlinear fields; the Sanders–Koiter equations are strongly simplified neglecting in-plane circumferential normal strains and tangential shear strains. The model is fully validated by means of comparisons with experiments, molecular dynamics data and finite element analyses obtained from the literature. Several types of nanotubes are considered in detail by varying aspect ratio, chirality and boundary conditions. The analyses are carried out for a wide range of frequency spectrum. The strength and weakness of the proposed approaches are shown; in particular, the model shows great accuracy even though it requires minimal computational effort
Eigenfrequencies and vibration modes of carbon nanotubes
No full textIn 1991 Iijima discovered Carbon Nanotubes, he synthesised molecular carbon structures in the form of fullerenes and then reported the preparation of a new type of finite carbon structure consisting of needle-like tubes, the carbon nanotubes, described as helical microtubules of graphitic carbon.
Examples of applications of Carbon Nanotubes (CNTs) can be found in ultrahigh frequency nanomechanical resonators, in a large number of nanoelectromechanical devices such as sensors, oscillators, charge detectors and field emission devices. The reduction of the size and the increment of the stiffness of a resonator magnify its resonant frequencies and reduce its energy consumption, improving its sensitivity.
The modal analysis of carbon nanotubes is important because it allows to obtain the resonant frequencies and mode shapes, which influence the mechanical and electronic properties of the nanotube resonators.
A large number of experiments and atomistic simulations were conducted both on single-walled (SWNTs) and multi-walled carbon nanotubes (MWNTs).
The present work is concerned with the analysis of low-frequency linear vibrations of SWNTs: two approaches are presented: a fully analytical method based on a simplified theory and a semi-analytical method based on the theory of thin walled shells.
The semi-analytical approach (shortly called “numerical approach”) is based on the Sanders-Koiter shell theory and the Rayleigh-Ritz numerical procedure. The nanotube deformation is described in terms of longitudinal, circumferential and radial displacement fields, which are expanded by means of a double mixed series based on Chebyshev polynomials for the longitudinal variable and harmonic functions for the circumferential variable. The Rayleigh-Ritz method is then applied to obtain numerically approximate natural frequencies and mode shapes.
The second approach is based on a reduced version of the Sanders-Koiter shell theory, obtained by assuming small ring and tangential shear deformations. These assumptions allow to condense both the longitudinal and the circumferential displacement fields. A fourth-order partial differential equation for the radial displacement field is derived. Eigenfunctions are formally obtained analytically, then the numerical solution of the dispersion equation gives the natural frequencies and the corresponding normal modes.
The methods are fully validated by comparing the natural frequencies of the SWNTs with data available in literature, namely: experiments, molecular dynamics simulations and finite element analyses. A comparison between the results of the numerical and analytical approach is carried out in order to check the accuracy of the last one.
It is worthwhile to stress that the analytical model allows to obtain results with very low computational effort. On the other hand the numerical approach is able to handle the most realistic boundary conditions of SWNTs (free-free, clamped-free) with extreme accuracy. Both methods are suitable for a forthcoming extension to multi-walled nanotubes and nonlinear vibrations
Nonlinear vibrations and energy distribution of carbon nanotubes
No full textThe nonlinear vibrations of Single-Walled Carbon Nanotubes are analysed. The Sanders-Koiter elastic shell theory is applied in order to obtain the elastic strain energy and kinetic energy. The carbon nanotube deformation is described in terms of longitudinal, circumferential and radial displacement fields. The theory considers geometric nonlinearities due to large amplitude of vibration. The displacement fields are expanded by means of a double series based on harmonic functions for the circumferential variable and Chebyshev polynomials for the longitudinal variable. The Rayleigh-Ritz method is applied to obtain approximate natural frequencies and mode shapes. Free boundary conditions are considered. In the nonlinear analysis, the three displacement fields are re-expanded by using approximate eigenfunctions. An energy approach based on the Lagrange equations is considered in order to obtain a set of nonlinear ordinary differential equations. The total energy distribution of the shell is studied by considering combinations of different vibration modes. The effect of the conjugate modes participation is analysed
Energy localization in carbon nanotubes
No full textIn this paper, the energy localization phenomena in low-frequency nonlinear oscillations of single-walled carbon nanotubes (SWNTs) are analysed. The SWNTs dynamics is studied in the framework of the Sanders-Koiter shell theory. Simply supported and free boundary conditions are considered. The effect of the aspect ratio on the analytical and numerical values of the localization threshold is investigated in nonlinear field
Ong on specific performance
No full textProfessor Denis Ong, author of the acclaimed works Trusts Law and Ong on Equity, addresses the complexities of Specific Performance in this book. In this erudite text, Professor Ong applies a forensic knowledge of the relevant case law, across Australian and international jurisdictions, resulting in a comprehensive analysis of Specific Performance.Key principles of law are identified and the key cases discussed in detail, often critically but always pinpointing the most relevant parts of judgments for readers
Don Denis. Poesie d'amore. Edizione commentata.
No full textThe study consists of a comment edition of 127 don Denis’ s love poems, conventionally divided into two sections: 75 cantigas de amor and 52 cantigas de amigo. Following the only complete edition of don Denis of Portugal (1261-1325), prepared by H. Lang in 1894, I proceeded to a textual revision, based on a systematic review of the codices and on the successive exegetical studies. The first aim of this revised critical edition is to offer an analytical comment of the poetical corpus of don Denis, the most representative author of the galician-portuguese poetry. The rich inquiry examines in detail any poem of the king poet from a thematic and rhetorical perspective and it documents the intertextual relations with the provençal and north french lyric on the one hand and the galician-portuguese poetry on the other.La tesi consiste in un’ampia edizione commentata dei 127 componimenti di tematica amorosa di don Denis di Portogallo (1261-1325), tradizionalmente ripartiti in 75 cantigas de amor e 52 cantigas de amigo. Sulla base dell’unica edizione critica completa della produzione poetica dionigina, quella allestita da H. Lang nel 1894, si è proceduto ad un’accurata revisione testuale del corpus, sia attraverso un controllo sistematico della tradizione manoscritta, sia prendendo in considerazione le recensioni e i successivi contributi critici. Ne risulta un’edizione criticamente rivista che si pone come obiettivo principale quello di offrire un analitico commento esegetico-critico ai singoli testi del re trovatore, unanimamente riconosciuto come il poeta più colto e rappresentativo della lirica galego-portoghese, ma al quale non sono stati finora dedicati studi monografici esaustivi. L’esteso commento rende dunque conto degli aspetti tematici, metrici, retorici e linguistici delle differenti poesie, nonché della fitta trama intertestuale che collega alcune di esse alla tradizione della lirica cortese (provenzale e francese) da un lato e al trobadorismo peninsulare dall’altro
The Ernst Denis Monument in Lesser Town Square
No full textThe segment from the 1928 weekly Elektajournal Issue No. 3 shows events preceding the installation and subsequent unveiling of a monument to the French historian and Slavicist Ernest Denis in Lesser Town Square (Malostranské náměstí) in Prague. Members of the Society for the Construction of Denis´s Monument use a maquette to find the best place for the statue. The event is attended by the author of the monument, sculptor Karel Dvořák. A shot of the author Dvořák in his studio, located in the courtyard of a house on Janáček Embankment (Janáčkovo nábřeží) in Smíchov, Prague. Digging works for the pedestal followed by shots from a segment from the 1928 weekly Elektajournal Issue No. 45 featuring the unveiling of the memorial on 27 October 1928, the eve of the 10th anniversary of the Czechoslovak Republic. President Tomáš Garrigue Masaryk, Minister of Education Milan Hodža, Prague Mayor Karel Baxa, General Jan Syrový, member of Parliament Antonín Uhlíř, French General Eugene Mittelhauser, French politician Alfred Oberkirch, and others are present on the stage. A speech by Minister of Foreign Affairs Edvard Beneš. A shot of President T. G. Masaryk and Edvard Beneš
Ong on equity
No full textOng on Equity is a substantial and sophisticated work from Professor Denis Ong, author of the acclaimed commentary: Trusts Law in Australia, now in its third edition. Ong on Equity analyses in detail relevant cases from all the Australian and from international jurisdictions and thoroughly reviews all aspects of judicial decision making.Importantly, Professor Ong considers unanswered questions as they arise in judicial reasoning in an incisive and learned style and offers fresh insights and thoughtful scholarly analysis in respect of each of the topics comprehensively covered in this volume
La crise, l’industrie et la finance (crisis, industry and finance)
No full textCe document analyse la crise dans l’industrie. Les uns après les autres pays et branches industrielles, sont durement touchés par des suppressions d’emploi dont l’ampleur donne le vertige. Dans les années 80, le monde de l’industrie a été bouleversé. Le modèle économique des groupes industriels repose sur une combinaison des activités industrielles et financières. Ce modèle, ici détaillé, met ces groupes à la merci des marchés financiers. La crise du crédit conjuguée à la baisse du revenu disponible a transformé la crise financière en crise économique de surproduction. Cet article présente les réactions des directions de grands groupes face à la crise à partir d’exemples précis. La situation financière de ces groupes est aussi analysée, et notamment l’importance à la fois des bénéfices réalisés et du poids de leur dette. Enfin, l’auteur aborde ce qu’il estime être des facteurs d’aggravation de la crise. Une fois de plus, la variable d’ajustement des comptes des grands groupes est essentiellement la force de travail, son effectif, et son taux horaire. Denis Langlet est l’auteur du livre « L’industrie dans la tourmente de la finance » édité chez l’Harmattan en mai 2008. This article analyses the economic crisis. In each country and each industrial branch, more and more companies lay off thousand and thousand workers. During 80’s years, the industrial world was greatly upset. The culture of the firms is boundaryless, outsourcing, subcontracting, cost reduction and merger/acquisitions. This economic model put the firms under the monetary founds pression. The monetary crisis and the fall of the disposable income change the situation: financial crisis become economical and global crisis. This article presents the top management declarations about this crisis and their commitment towards shareholders. The financial situation of these groups and their huge debt are pointed. Then, the author speaks about the cost reduction policy whose the first target is the working class. Denis Langlet is the author of the book untitled “L’industrie dans la tourmente de la finance” edited by L’Harmattan in 2008 may.crisis, industry, firm, finance, shareholders
La santé au travail comme thème d'action militante : l'expérience des groupes C.O.S.H. aux États-Unis
No full textDenis Duclos
Health at the workplace as a cause for militant action : the experience of the Committees on Occupational Safety Health and in the United States of America.
Alternative, anti-establishment politics in the US during the last decade took various forms, among them the defense of certain public interest causes. The author chose to study the Committees on Occupational Safety and Health (COSHs), defined as action groups providing technical assistance, training and political lobbying. These groups maintained a high degree of autonomy, while collaborating with labor unions on issues of health and safety at the workplace.
The analysis of the forms their action took and the way in which these developed over time shows the originality (as compared to France) of a social movement, in particular as concerns its capacity to survive despite the weakness of its institutional ties with unions, government and the legal system.Parmi les formes d'insertion sociale du radicalisme américain porté, au cours de la dernière décennie, par la montée diverse des contestations, on peut placer l'engagement dans certains rôles d'animation de causes collectives.
L'auteur choisit d'étudier l'une de ces expériences militantes : les C.O.S.H. (Committees on Occupational Safety and Health), définis comme des groupes d' assistance technique, d'éducation et de «lobbying» politique s' organisant, de manière indépendante mais en liaison avec les organisations syndicales, sur les questions de santé et de sécurité au travail.
L'analyse de ses formes d'action et de leurs évolutions révèle l'originalité, par rapport à la France, d'un mouvement, en particulier, dans sa capacité à se perpétuer malgré sa faible inscription institutionnelle au plan syndical, administratif ou juridique.Duclos Denis. La santé au travail comme thème d'action militante : l'expérience des groupes C.O.S.H. aux États-Unis. In: Sociologie du travail, 26ᵉ année n°2, Avril-juin 1984. pp. 177-194
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