1,721,062 research outputs found
Interaction of short-wavelength laser pulses with matter on various time scales
No full textAn advent of powerful sources producing intense and ultrashort laserpulses containing high-energy photons opened up a wide range of possibilitiesto conduct experiments formerly achievable only through theoretical calculationsand models. This thesis provides a complex overview of processes which occurright after arrival of the first photons, through lattice heating, up to resolidifica-tion and formation of irreversible changes. Irradiated spots and craters formed invarious materials are examined employing a wide range of microscopic and spec-troscopic methods which provide a deep insight into laser-induced modificationssuch as detachment of a graphene layer from SiC substrate or thermally-induceddiffusion of tellurium inclusions through CdTe lattice. An increased emphasisis placed on beam characterization utilizing ablation and desorption imprints insuitable solids. A proper knowledge of the beam fluence profile may serve forevaluation of diverse damage thresholds as well as for modelling of the pulsepropagation or consequent retrieval of otherwise unmeasurable opacity of warmdense aluminium plasma heated to temperatures exceeding tens of thousands ofKelvins. Moreover, the method of desorption imprints is extended to accuratecharacterization of pulses delivered at MHz repetition rate. This work aims tocontribute to general understanding of interaction between short-wavelength laserpulses and matter at different time scales
Interakce krátkovlnných laserových impulsů s hmotou v různých časových škálách
No full textPříchod výkonných zdrojů produkujících intenzivní a krátkovlnné laserové impulsy obsahující vysokoenergetické fotony s sebou přinesl širokou škálu možností pro realizaci experimentů, jež byly dříve dostupné pouze skrze teoretické výpočty a modely. Tato práce přináší komplexní přehled procesů odehrávajících se bezprostředně po příchodu prvních fotonů, přes zahřívání krystalové mřížky, až po resolidifikaci a formaci nevratných změn. Ozářená místa a krátery vytvořené v různých materiálech jsou zkoumány za využití několika mikroskopických a spektroskopických metod, které poskytují výborný náhled do laserem indukovaných přeměn, jako je odtržení grafénové vrstvy od SiC substrátu či tepelně indukovaná difúze telurových inkluzí skrze mřížku CdTe. Zvýšený důraz je kladen na charakterizaci laserových svazků za použití ablačních a desorpčních otisků ve vhodných materiálech. Dobrá znalost fluenčního profilu svazku může posloužit nejen k určení rozličných prahů poškození, ale i při modelování propagace impulzu prostředím. S jeho pomocí lze získat jinak neměřitelnou absorpci v teplém hustém hliníkovém plazmatu zahřátém na teploty přesahující desítky tisíc stupňů Kelvina. Metoda desorpčních otisků je zde navíc rozšířena o přesnou charakterizaci impulzů přicházejících na megahertzové opakovací frekvenci. Cílem...An advent of powerful sources producing intense and ultrashort laser pulses containing high-energy photons opened up a wide range of possibilities to conduct experiments formerly achievable only through theoretical calculations and models. This thesis provides a complex overview of processes which occur right after arrival of the first photons, through lattice heating, up to resolidification and formation of irreversible changes. Irradiated spots and craters formed in various materials are examined employing a wide range of microscopic and spectroscopic methods which provide a deep insight into laser-induced modifications such as detachment of a graphene layer from SiC substrate or thermally-induced diffusion of tellurium inclusions through CdTe lattice. An increased emphasis is placed on beam characterization utilizing ablation and desorption imprints in suitable solids. A proper knowledge of the beam fluence profile may serve for evaluation of diverse damage thresholds as well as for modelling of the pulse propagation or consequent retrieval of otherwise unmeasurable opacity of warm dense aluminium plasma heated to temperatures exceeding tens of thousands of Kelvins. Moreover, the method of desorption imprints is extended to accurate characterization of pulses delivered at MHz repetition rate....Fyzikální ústav UKInstitute of Physics of Charles UniversityMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Soft remnant interactions and rapidity gaps
No full textSoft colour exchange models give a unified description of both diffractive and non-diffractive events, such that e-p and p-pbar collider data with and without rapidity gaps are well reproduced. We show that these models also describe the new Tevatron data</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
