Electromechanical fields in a hollow piezoelectric cylinder under non-uniform load: flexoelectric effect

2021 ◽  
pp. 108128652110207
Author(s):  
Olha Hrytsyna

The relations of a local gradient non-ferromagnetic electroelastic continuum are used to solve the problem of an axisymmetrical loaded hollow cylinder. Analytical solutions are obtained for tetragonal piezoelectric materials of point group 4 mm for two cases of external loads applied to the body surfaces. Namely, the hollow pressurized cylinder and a cylinder subjected to an electrical voltage V across its thickness are considered. The derived solutions demonstrate that the non-uniform electric load causes a mechanical deformation of piezoelectric body, and vice versa, the inhomogeneous radial pressure of the cylinder induces its polarization. Such a result is obtained due to coupling between the electromechanical fields and a local mass displacement being considered. In the local gradient theory, the local mass displacement is associated with the changes to a material’s microstructure. The classical theory does not consider the effect of material microstructure on the behavior of solid bodies and is incapable of explaining the mentioned phenomena. It is also shown that the local gradient theory describes the size-dependent properties of piezoelectric nanocylinders. Analytical solutions to the formulated boundary-value problems can be used in conjunction with experimental data to estimate some higher-order material constants of the local gradient piezoelectricity. The obtained results may be useful for a wide range of appliances that utilize small-scale piezoelectric elements as constituting blocks.

2020 ◽  
pp. 108128652096337
Author(s):  
Olha Hrytsyna

The size-dependent behaviour of a Bernoulli–Euler nanobeam based on the local gradient theory of dielectrics is investigated. By using the variational principle, the linear stationary governing equations of the local gradient beam model and corresponding boundary conditions are derived. In this set of equations the coupling between the strain, the electric field and the local mass displacement is taken into account. Within the presented theory, the process of local mass displacement is associated with the non-diffusive and non-convective mass flux related to the changes in the material microstructure. The solution to the static problem of an elastic cantilever piezoelectric beam subjected to end-point loading is used to investigate the effect of the local mass displacement on the coupled electromechanical fields. The obtained solution is compared to the corresponding ones provided by the classical theory and strain gradient theory. It is shown that the beam deflection predicted by the local gradient theory is smaller than that by the classical Bernoulli–Euler beam theory when the beam thickness is comparable to the material length-scale parameter. The obtained results also indicate that the piezoelectricity has a significant influence on the electromechanical response in a dielectric nanobeam. The presented mathematical model of the dielectric beam may be useful for the study of electromechanical coupling in small-scale piezoelectric structures.


2021 ◽  
Author(s):  
Julissa Rojas-Sandoval

Abstract L. inermis is a small, multi-stemmed shrub or small tree 2-6 m tall, commonly known as henna. It originates from the Persian Gulf region (and possibly northeast Africa) to northwest India and is now cultivated widely throughout the tropics and subtropics. The leaves produce a red dye which is used to paint fingernails, to decorate the body and to dye hair. Henna dye is very important traditionally, being used in Muslim and Hindu marriage ceremonies. In the past, its leaves were widely used to dye silk and wool, and less commonly cotton and leather. The wood of L. inermis is fine-grained and hard, being used for tent pegs and tool handles. A perfume is made from the flowers. Extracts from the leaves (and to a lesser extent the roots) are used in traditional medicine as a panacea against almost any disease. L. inermis is mostly grown on a small scale in gardens (often as a hedge) but is grown commercially in India, Pakistan, Egypt, Libya and Sudan. In African plantations, it is often irrigated and fertilized. It is easily grown as a short-lived perennial crop from seed and transplanted, or propagated by cuttings. It is adapted to a wide range of environmental conditions, but requires high temperatures for good growth. Henna is an important natural dye. To increase the potential of the crop, selection and breeding are needed to increase the content of the pigment lawsone (2-hydroxy-1,4-naphthoquinone) in the leaves. Many cultivars already exist locally, having being selected for their leaves or flowers. Research is also neeeded on ways to improve drying and processing of the leaves.


2017 ◽  
Vol 63 (6) ◽  
pp. 1083-1093 ◽  
Author(s):  
David S Hage

Abstract BACKGROUND The interactions between biochemical and chemical agents in the body are important in many clinical processes. Affinity chromatography and high-performance affinity chromatography (HPAC), in which a column contains an immobilized biologically related binding agent, are 2 methods that can be used to study these interactions. CONTENT This review presents various approaches that can be used in affinity chromatography and HPAC to characterize the strength or rate of a biological interaction, the number and types of sites that are involved in this process, and the interactions between multiple solutes for the same binding agent. A number of applications for these methods are examined, with an emphasis on recent developments and high-performance affinity methods. These applications include the use of these techniques for fundamental studies of biological interactions, high-throughput screening of drugs, work with modified proteins, tools for personalized medicine, and studies of drug–drug competition for a common binding agent. SUMMARY The wide range of formats and detection methods that can be used with affinity chromatography and HPAC for examining biological interactions makes these tools attractive for various clinical and pharmaceutical applications. Future directions in the development of small-scale columns and the coupling of these methods with other techniques, such as mass spectrometry or other separation methods, should continue to increase the flexibility and ease with which these approaches can be used in work involving clinical or pharmaceutical samples.


Author(s):  
Maziar Janghorban ◽  
Behrouz Karami

Background:: Carbon nanotubes (CNTs) reinforced structures are the main elements of structural equipment. Hence a wide range of investigations has been performed on the response of these structures. A lot of studies covered the static and dynamic phenomenon of CNTs reinforced beams, plates and shells. However, there is no study on the free vibration analysis of a doubly-curved nano-size shell made of CNTs reinforced composite materials. Methods:: This work utilized a general third-order shear deformation theory to model the nanoshell where the general strain gradient theory is used in order to capture both nonlocality and strain gradient size-dependency. The Navier solution solving procedure is adopted to solve the partial differential equations (PDEs) and get the natural frequency of the system which is obtained through the Hamilton principle. Results:: The current study shows the importance of small-scale coefficients. The natural frequency increases with rising the strain gradient-size dependency which is because of stiffness enhancement, while the natural frequency decreases by increasing the nonlocality. In addition, the numerical examples covered the CNTs distribution patterns. Conclusion:: This work also studied the importance of shell panel’s shape. It has been observed that spherical shell panel has a higher frequency compared to the hyperbolic one. Furthermore, the frequency of the system increases with growing length-to-thickness ration.


2018 ◽  
Vol 12 (1) ◽  
pp. 151-170
Author(s):  
Hannah Vandegrift Eldridge

Abstract In recent years, theories of rhythm have been proposed by a number of different disciplines, including historical poetics, generative metrics, cognitive literary studies, and evolutionary aesthetics. The wide range of fields indicates the transdisciplinary nature of rhythm as a phenomenon, as well as its complexity, highlighting the degree to which many of the central questions surrounding rhythm remain extraordinarily difficult even to state in terms that can traverse the disciplinary boundaries effortlessly transgressed by rhythm as a phenomenon. In particular, any theory of rhythm, whether in music, dance, sociology, or language, must grapple with two quandaries. First, the precise site of rhythm remains opaque: rhythms occur in, affect, and are produced by all of bodies, cultures, and universals (whether metaphysical or species-physiological). What is the relation between species-wide characteristic, individual body, cultural context, and the history of art making in the experience of rhythm? Second, rhythm is simultaneously a phenomenon of fixed, organizing form and one of dynamic, changing flow. How can rhythm encompass both the measurement of regular recurrences across time and the organizing of temporal phenomena as they unfold? In this article, I draw on Emile Benveniste and Henri Meschonnic to elucidate these quandaries or conflicts before turning to Friedrich Nietzsche’s work on rhythm. I argue that Nietzsche’s work with rhythm provides a historically situated model for how we might continue to take the questions and conflicts within rhythm seriously, rather than privileging an abstract and universally applicable theory of rhythm. This model is especially crucial for our own historical moment, when cultural-political emphasis on science and technology at the expense of aesthetics devalues all insights not presented in the form of countable data points or empirically testable facts. Nietzsche is, of course, one of the great critics of positivist-scientistic epistemologies, part of a long tradition questioning the naturalness of natural-scientific paradigms and alerting us to the metaphors at play even in the ›hard sciences‹. I use rhythm as one paradigmatic place to resist the importation of scientistic thought into discussions of language, literature, and culture. I show how Nietzsche’s writings on rhythm prove illuminating for contemporary understandings of rhythm because the tensions in his work are shaped by the quandaries inherent to rhythm that I have used Benveniste and Meschonnic to elaborate, namely the question of rhythm’s site as individual, cultural, or universal, and the conflict between rhythm as form and as flow. The question of the site of rhythm appears in Nietzsche’s discussions of Greek and Latin meters both in his philological works, in his aphorisms, and in his letters: on the one hand, he argues that Greek and Latin metrical and rhythmic resources are irrevocably lost to modern cultures (indicating that rhythm is a product of culture), while on the other, he emphasizes the impact of rhythm on the body and offers advice for replicating Ancient metrical and rhythmic techniques (suggesting that rhythm is based on physiological universals). And the conflict between flow and form appears as Nietzsche praises both the productive constraint created by large-scale, architectonic, or macro-formal rhythms and the freedom from such constraint enabled by small-scale, leitmotiv-based, or micro-formal rhythms. The conflicts in Nietzsche’s work between the loss and recovery of Ancient rhythms and between rhythm as small scale freedom vs. large scale constraint thus represent one particular unfolding of the dilemmas for rhythmical theory worked out by Benveniste and Meschonnic. The various modern disciplines engaged with rhythm will answer different sets of these questions in different ways. Most practitioners of, e. g., evolutionary aesthetics, neuroaesthetics, or cognitive poetics would no doubt contend that they are using the tools of the natural sciences to investigate long-standing humanistic inquiries. Nietzsche, as a critic of his own era’s scientific positivism who allows tensions inherent in these questions to remain open in his own work, is an ideal interlocutor with whom to ask whether even the adoption of these tools ends up placing excessive faith in natural-scientific paradigms and undercutting other—affective, bodily, metaphorical, poetic, etc.—ways of knowing, as I demonstrate briefly in the examples of evolutionary aesthetics and generative metrics. Because Nietzsche leaves open the conflicts over rhythm’s site and its qualities as form or flow, he can use individual bodily experience to make physiological arguments about the effects of rhythm on culture and vice versa: Nietzsche takes his bodily response to be an index of cultural values inherent to rhythmical practices. The particular values that Nietzsche critiques shift across his career—early on he condemns German musical and poetic rhythms for being too rigid, while later he sees them as pathologically heightening affect and emotion. In both cases, detrimental rhythmic practices lead to detrimental bodily practices and to the degeneration of culture, while rhythmic practices work as a bodily and cultural corrective. In his critiques of German forms and praises of Greek forms, and in the moments in which he brings them together, Nietzsche thus asserts the complex interrelation of culture, body, and history.


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