251 research outputs found
Theoretical treatment of ultrashort pulse laser processing of transparent materials: What is energetically and mechanically meaningful?
No full textUltrashort laser pulses are a powerful tool for modifying the structure and properties of transparent materials. Depending on material properties and irradiation conditions, a wide variety of modifications can be induced such as surface and bulk periodic structures (nanogratings), densification with associated refractive index change, microvoids and void chains, phase transitions, etc. This gives rise to numerous technological applications based on 3D photonic structures in bulk optical materials (waveguides, Bragg gratings, Fresnel zone plates, rewritable optical memories, and others). Among transparent materials, optical glasses are of prime importance for optoelectronics and photonics due to their relatively low cost, processability, and possibility of governing refractive index and inducing optical anisotropy. The physics behind laser-induced glass modifications is extremely rich and involves the multiplicity of the consecutive processes initiated by radiation absorption during the laser pulse and extending to millisecond time scales when the final structure becomes “frozen” in the glass matrix. While tremendous achievements have been made toward laser-writing techniques and assembling integrated optics, the physical mechanisms underlying glass modifications have not been fully understood. The exigency of controllable generation of desired structures requires deeper insight into of the mechanisms and spatiotemporal dynamics of laser-induced glass transformations.In this report, we will review the physical processes and mechanisms responsible for various forms of glass modification. Different approaches for modeling ultrashort laser pulse propagation in transparent materials will be critically assessed. The dynamics of laser-induced creation of free electron plasma inside bulk glass will be analyzed, depending on the irradiation conditions. A contradictory issue on the free electron density generated in glass materials upon laser irradiation will be addressed with reviewing the existing theoretical results and experimental evaluations based on application of the Drude theory. The results of modeling will be presented obtained on the basis of the Maxwell’s equations supplemented with the equations describing electron plasma generation and the laser-induced electric current. We will demonstrate that the model allows following important features of laser beam propagation in the regimes of tight focusing and dense electron plasma generation when unidirectional approximations such as the non-linear Schrödinger equation do not provide adequate description. Based on this model we have studied spatiotemporal dynamics of laser beam propagation with self-focusing, free electron generation, and plasma-induced defocusing on the example of fused silica glass under particular irradiation regimes employed for laser direct writing. As a result, the geometry of the laser energy absorption zone is determined and the glass temperature is mapped which may be foreseen at the end of electron – glass matrix relaxation. This, in turn, allows estimating the laser-induced stress levels and making conclusions on the routes of glass modification. Finally, based on the performed analysis, we consider the energy balance, matching the free electron energy and temperature with several threshold values (melting, plastic deformation, material failure with void formation, sublimation).*This research is supported by Marie Curie International Incoming Fellowship grant of the corresponding author, No. 272919
Ideias de L. S. Vigotski sobre a ciência do desenvolvimento infantil
No full textNeste artigo, analisam-se as ideias principais da quarta conferência de Vigotski, "A questão do meio na pedologia", no contexto da série de sete conferências intitulada "Fundamentos de pedologia", e outros trabalhos do autor sobre o mesmo tema. Essa série é considerada como representativa do projeto de Vigotski para uma ciência do desenvolvimento infantil. A quarta conferência enfoca principalmente as tendências específicas do desenvolvimento psicológico. Mostra-se que as ideias dessa conferência foram posteriormente desenvolvidas no trabalho "O problema da idade" e em leituras concernentes à crise da idade
Shock-induced structural instability and dynamic strength of metals
No full textAbstractThe shock tests of set of metals show that together with well-known dynamic strength-characteristics of material such as dynamic yielding limit and spall strength, the additional characteristics, namely, threshold of structural instability under shock compression, defect of the velocity at the plateau of compressive pulse and particle velocity variance at the mesoscale should be introduced into analysis of dynamic strength of materials. The structural instability threshold registered in uniaxial strain conditions allows the resistance to penetration in Tate-Alekseevskii equation to be determined
The Meiji Revolution: 100 and 150 Years Later (Nikolai Konrad and the Paradoxes of His “Progress”)
No full textUsing the example of the article “The Centenary of the Japanese Revolution” (1968) by the outstanding Japanologist Nikolai Konrad, the author examines his understanding of the “Meiji Revolution”. Holding on, by and large, to the Marxist views on history, Nikolai Konrad turned out to be surprisingly close to “bourgeois” historians in understanding the Meiji Revolution. The “bourgeois” and Soviet historians (including Konrad himself), who were in conflict relations, consistently qualified the Meiji Revolution as a “progressive” (positive) event that introduced Japan to the “world” (i.e., Western and the only one possible) civilization. Marxist and “bourgeois” thinkers differed in their assessment of the future (whether or not communism was the highest stage of progress), but their view of the Japanese past showed amazing unanimity. The keenness on the theory of progress was so allembracing that Nikolai Konrad’s assessments of specific historical phenomena of the Tokugawa period demonstrate outright error and bias. None of the “advanced” European countries could boast of such a long-lasting social peace as that which we observe in the Tokugawa period, which, however, did not prevent Konrad (as well as other Western historians) from branding the Tokugawa rule as “reactionary” and “stagnant”
Finding One’s Identity: Fukuzawa Yukichi About His Studies in Osaka (Chapter “Ogata School” From “The Autobiography of Elder Fukuzawa”)
No full textFukuzawa Yukichi (1835–1901) is rightly considered a person who made a significant contribution to introducing Western civilization to Japan. His writings on politics, society, state, pedagogy, i.e., products of “mature” Fukuzawa, are often being studied. However, Fukuzawa’s personality itself usually remains outside the scope of such studies. But it seems extremely important to understand how the personality of this outstanding educator, who dared to raise his hand against the fundamental values of the state and society of the Tokugawa era, was formed. This will allow us to understand not only Fukuzawa himself, but also the type of person who was in demand during the time of revolutionary change.In 1899 Fukuzawa published his autobiography (Fukuō Jiden). It is considered the first “full-fledged” work of the autobiographical genre in Japan. In this text, with unprecedented frankness for former Japan, the author talks about himself. Fukuzawa dictated the text to a stenographer, so his publication has all the usual properties of spontaneous oral speech: liveliness, vulgarisms, factual errors, repetitions, contradictory statements, spontaneity and some randomness. This does not change the fact that Fukuzawa was an observant man and an excellent storyteller. A significant part of the “Autobiography” is devoted to his childhood and youth, that is, the time when the formation of one’s personality occurs.In this publication, we provide a translation of a chapter dedicated to Fukuzawa’s studies at the Osaka School of Medicine, which was opened by Ogata Kōan (1810–1863), a famous doctor who practiced European medicine. About three thousand people graduated from his school. In Fukuzawa’s description, the students at this school were characterized by deviant behavior, which provided them with an identity different from the personality type that prevailed in Tokugawa Japan. Many graduates of the Ogata school later became famous and had a significant influence on the appearance of the new Japan, which was significantly different from the old Japan
Evolution and Culture
No full textThe goal of cross-cultural psychology to identify and explain similarities and differences in the behavior of individuals in different cultures requires linking human behavior to its context (Cole, Meshcheryakov & Ponomariov, 2011). In order to specify this relation, the focus is usually on the sociocultural environment and how it interacts with behavior. Since cross-cultural psychology also deals with the evolutionary and biological bases of behavior, this focus on culture has regularly led to an unbalanced view (Berry, Poortinga, Breugelmans, Chasiotis & Sam, 2011). Too often, biology and culture are seen as opposites: what is labeled as cultural is not biological and what is labeled as biological is not cultural (Chasiotis, 2010, 2011a). This article will first introduce the central concepts of natural and sexual selection, adaptation, and the epigenetic (open) genetic processes in evolutionary biology, and indicate their psychological implications. It will then argue that biology and culture are intricately related. Finally, empirical evidence from diverse psychological research areas will be presented to illustrate why the study of the evolutionary basis is as essential as the analysis of the sociocultural context for the understanding of behavior. Due to space restrictions, cultural transmission will be the only research area which is addressed in more detail (more examples of evolutionary approaches in intelligence, personality, and behavior genetics and their implications for cross-cultural research can be found on the website accompanying Berry et al., 2011; see also further readings section)
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