1,095 research outputs found

    Preparation and Thermoluminescence Properties of Polycrystalline Na2SO4/SiO2 composite

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    A sodium sulphate/silica (Na2SO4/SiO2) composite was prepared by a sol-gel procedure using a geode as the silica source. The prepared sample was characterized by XRD, XRF and IR techniques. The Na2SO4/SiO2 has an orthorhombic phase, and an average crystalline size is about 51 nm. Thermoluminescence characteristics of Na2SO4/SiO2 were studied at different parameters. The glow curve resulting from Na2SO4/SiO2 showed one clear peak between 150 oC to 200 oC, depending on the energy. The general peak structure of the TL glow curve remains unchanged as a result of repeated cycles of irradiation at various X–ray energies, and exhibits good linearity over the used exposure. There were no significant changes in the TL reading after ten times of reuse, and the fading was observed at 56% after 15 days of irradiation and after one month about 82.3% of the TL signal was lost, and the value of Zeff of Na2SO4/SiO2 was found to be 13.56

    Designs of Blackness

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    Across more than two centuries Afro-America has created a huge and dazzling variety of literary self-expression. Designs of Blackness provides less a narrative literary history than, precisely, a series of mappings—each literary-critical and comparative while at the same time offering cultural and historical context. This carefully re-edited version of the 1998 publication opens with an estimation of earliest African American voice in the names of Phillis Wheatley and her contemporaries. It then takes up the huge span of autobiography from Frederick Douglass through to Maya Angelou. "Harlem on My Mind," which follows, sets out the literary contours of America’s premier black city. Womanism, Alice Walker’s presiding term, is given full due in an analysis of fiction from Harriet E. Wilson to Toni Morrison. Richard Wright is approached not as some regulation "realist" but as a more inward, at times near-surreal, author. Decadology has its risks but the 1940s has rarely been approached as a unique era of war and peace and especially in African American texts. Beat Generation work usually adheres to Ginsberg and Kerouac, but black Beat writing invites its own chapter in the names of Amiri Baraka, Ted Joans and Bob Kaufman. The 1960s has long become a mythic change-decade, and in few greater respects than as a black theatre both of the stage and politics. In Leon Forrest African America had a figure of the postmodern turn: his work is explored in its own right and for how it takes its place in the context of other reflexive black fiction. "African American Fictions of Passing" unpacks the whole deceptive trope of "race" in writing from Williams Wells Brown through to Charles Johnson. The two newly added chapters pursue African American literary achievement into the Obama-Trump century, fiction from Octavia Butler to Darryl Pinkney, poetry from Rita Dove to Kevin Young

    Operadic Deformation Theory

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    This is a survey on recent progress in algebraic deformation theory from the point of view of Koszul duality of algebraic operads.Comment: 95 page

    Daylight entanglement-based quantum key distribution with a quantum dot source

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    Entanglement-based quantum key distribution can enable secure communication in trusted node-free networks and over long distances. Although implementations exist both in fiber and in free space, the latter approach is often considered challenging due to environmental factors. Here, we implement a quantum communication protocol during daytime for the first time using a quantum dot source. This technology presents advantages in terms of narrower spectral bandwidth-beneficial for filtering out sunlight-and negligible multiphoton emission at peak brightness. We demonstrate continuous operation over the course of three days, across an urban 270 m-long free-space optical link, under different light and weather conditions

    Formulation and Optimization of Algae-Filled Polylactic Acid Thermoplastic Compounds for Improved Biodegradation

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    Conventional plastics derived from non-renewable petrochemicals – especially from fossil reserves – have become an integral part of human life because their structure can be chemically manipulated to obtain a wide range of properties and geometries necessary in nearly all industries. The volume and rate at which petroleum plastics are produced, used, and discarded has incited several significant issues related to human health, environmental conservation, and ecological biodiversity. To address these issues, many institutions have begun investigating solutions in both the development and end-oflife phases of plastic production and waste. In this thesis, a Chlorella-dominated algae mixture is dried and compounded at varying ratios with polylactic acid (PLA) at various particle sizes. The resulting blends were then characterized by thermal and mechanical analysis to examine processing and performance properties for injection molding. The blends were subject to weathering studies via standardized test methods and found that at 10, 20, and 30 wt.% algae, the blends are biodegradable with the rate of biodegradation directly correlated to the increasing concentration of algae

    A critical analysis of the Kiba (song-dance-drama) discourse

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    1 Aim The aim of the research is to map out the theoretical construct of Kiba from practice. The analysis includes the mapping out of the metalanguage of the theory used by its practitioners. Therefore the research will map out a theory of Kiba not as a generic hypothetical theory of music and dance, but as a theory that describes actual performance. The research aims to achieve this not only through the description of what practitioners do in actual performance, but also through analysing the language behaviour and principles that govern the making of the performance discourse. The research will also look into the dynamic nature of culture and the challenges of ownership and rights that emerge. The analysis starts by tracing social practices and ethics that influence dance, drumming, music making, praise, and design of costume used in contemporary Kiba. It also looks at compositional structures, aesthetic elements, and principles governing the communicative competence of Kiba. The research presents the texts in Sepedi with English translations. It focuses on the description and analysis of principles governing the production and management of the discourse. Though the analysis focuses on the communicative function and value of Kiba, its main thrust is on principles that govern the making of the integral communication. The researcher uses mainly the performers' interpretation of the Kiba performance theory, as well as approaches to the analysis of cultural context of communication espoused by Hymes (1970) and Saville-Troike (1989). 2 Hypothesis If Kiba practice theory is not developed, then Kiba will not find access into the mainstream of Arts and Culture curricula at all levels of education. The chances of it competing successfully in economic markets of the Arts and Culture will not see the light of day. 3 Methods and procedures Kiba is a complex genre. The analysis of its performance discourse, that is, its dance-drama and praise-song of Kiba requires an interdisciplinary approach. This will be particularly useful in the analysis of the dance sequence structure with its dramatic effect, and of the principles governing the choices of repertoire and music elements. Barber (1989:13) supports this approach for the analysis of complex genres. She points out that: There is an obvious and very good reason for taking an interdisciplinary approach to African oral texts, and that is that the texts themselves can combine 'literature', 'history', 'music', 'religion' and other things. The unity of these fields within oral texts suggests that the method of interpretation should also be unified. Rather than collaboration between specialists from different disciplines, what is needed is the reintegration of an artificially divided field. It is crucial to state from the outset that the research does not perceive Kiba as music or art, but as a way of lived communication and it echoes the observation made by Agawu (2002: 452) that: ... in many African languages, there is no single word for 'music' that the term is semantically dispersed across many fields often indexing dancing or movement as well as the actual sound produced. However, since the overall vehicle of a Kiba performance is presented in songdance, the research will trace the 'musical' and not the 'music' elements of Kiba. Nevertheless it does make a conscious effort to strike a balance between the musical, literary, dance, and the philosophical. iii In Sepedi as well as the broad Sotho languages, the word for music is 'mmino'. This refers to both song and dance. This concept will be represented in the research as 'song-dance'. Therefore, a multidisciplinary approach to the study of Kiba will prove to be more useful than an approach to music or just dance elements of Kiba. An analysis of the co-operative principles that underpin the Kiba discourse, and the cultural and compositional elements of Kiba will form part of the interdisciplinary approach to the study of Kiba. The research will also use elements of sociolinguistics, cantometrics, ethnomethodology and ethnomusicology to analyse Kiba discourse. iv 4 Procedures: focus areas of the research The entire inquiry obtained data from participants through unstructured interviews and observation of the language behaviour of Kiba interlocutors. Observation and interviews were carried out in ten villages. The basic questions and the researcher's observation of live performance of Kiba focused on the three main areas of the research: compositional structure, aesthetic elements, and principles governing the actual performance. The latter refers to the norms and standards of interaction in, and interpretation of, Kiba discourse. The basic questions that are asked are: Definition of Kiba □ Kiba ke eng?I What is Kiba? ✓ A Kiba ke ya banna goba ke ya basadi?l ls Kiba a male or female genre? ✓ A Kiba ke ya baswa goba ke ya batho ba bagolo? /Is Kiba a youth or adult genre? Compositional and aesthetic elements: □ Ge le bina Kiba le dira eng? I What are the structural elements of Kiba? □ Mekgwa ya go natefisa kosa ke efe? /What are the ways of embellishing a song? □ Diletso tse di diriswago mo Kibeng ke dife? I What resources are used in the Kiba communication system? Which principles govern actual performance communication? Examine the following: □ Poledisano le kgolagano ya kosa magareng a malokwane le sehlopha, le magareng ga sehlopha le babogedi goba setshaba? I The discourse structure of the Kiba intra-communication system: analysis of the intercommunication strategies between the Kiba participants as addressers and an individual or a community as addressee(s). V □ A Kiba ke ya Bapedi goba ke Sepedi? Is Kiba a genre of the Bapedi or is it Sepedi? Translated texts appear beneath the original texts. Original texts appear in italics, while translations are typed in normal font as Mason (interview: Washington DC, June 1997) advises. Vernacular names and words are used and explained in context. Single word expressions and exclamations have been retained and their explanations are given in square brackets. A glossary of terms has been provided at the end of the thesis. 5 Abbreviated thesis Accompanying the research is an audio-visual presentation that shows the · prototype of an integral and fully expanded discourse of Kiba. The video is intended to help the reader and viewer to understand performance nuances of dance, drumming, voice technique, and the use of colour. The audiovisual excerpt of an exemplary performance of Kiba is provided as annexure 4. The latter is an authentic text that shows a royal ensemble, led by Chief Ramokgopa during his official visit to the royal capital of Moletsi on 1 January 1999. The excerpt shows every aspect of Kiba raised by the research. vi There are also accompanying compact discs, which reveal the conscious attempt to further develop Kiba into a modern competitive format called FreeKiba. (See the copies of the themes presented in annexure I, and the two CDs that are provided as part of annexure 4). Agawu (2002:47) perceives this kind of an adaptation as progressive in that it is premised on the agenda of the emancipation of African music. He puts it succinctly: The emancipation of African music begins precisely at the point where our priorities shift from valuing present realities to constructing future possibilities. This view is also held by Nzewi (1980, 1983). 6 Conclusion The research will use ethnomusicology to analyse participants' use of song, dance, drama, drumming and praise-singing as integral constituents of Kiba. To analyse the Kiba discourse structure, the research will use the 'ethnography of communication method. The method is useful in the analysis principles governing the appropriateness of lived communication (Hymes 1964). It also requires principles of ethnomethodology to be used to 'discover what methods [Kiba] practitioners use to participate in and make sense of interactions of thei

    Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038

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    Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to millisecond radio pulsars in binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray to optical pulsations are observed only during the high mode. The root cause of this puzzling behaviour remains elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar prototype, PSR J1023+0038, covering from the radio to X-rays. The campaign was carried out over two nights in June 2021 and involved 12 different telescopes and instruments, including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA, and FAST. By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with ALMA at the high-to-low mode switch. The pulsar is subsequently re-enshrouded, completing our picture of the mode switches.</p

    Semiconductor quantum dots for photonic quantum repeaters

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    Current information exchange is based on optical fibers and satellite communication via free-space links, where security is provided by mathematical complexity. However, it could potentially be threatened by paradigm shifts in computing technology. Encryption techniques using quantum key distribution based on entangled photons would allow for theoretical full secure communication. The very same platform, entangled photons, can also be employed as a core element to establish multi-node secure communication—a concept known as quantum network. For these reasons, en tangled photon sources might be the core of future quantum networks for secure communication. In this thesis, I study GaAs/AlGaAs quantum dots as entangled photon sources. After giving a general overview on the fundamentals of photonic quantum networks and GaAs droplet-etched quantum dots, I mainly focus on two aspects of the development of this technology. First, limits of the source performance as entangled photon sources and second, applications of entangled photons from quantum dots for secure communication. The prior includes degrading effects of entanglement in these quantum dots, especially based on multiphoton emission and optical Stark effect induced by the particular entangled-photon generation technique, resonant two-photon excitation. The experimental results demonstrate that multiphoton emission is negligible under practical conditions, which is supported by a probabilistic model. The finite excitation laser pulse duration in resonant two-photon excitation, on the other hand, induces an optical Stark effect. The measurements in this thesis support the theoretical predictions and an entanglement reduction by increasing excitation laser pulse length is observed experimentally. If some conditions are met, GaAs/AlGaAs quantum dots emit highly entangled photons, which are utilized in the second part of this thesis by applying them in entanglement-based quantum key distribution protocols. The demonstrations range from the first implementation of quantum dots as entangled photon sources for secure communication in fiber and free-space, to a continuous secret key exchange over three days. The second test case, in particular, tackles the challenges of real-life applications such as sunlight and mild rain. At the end, I provide a brief outlook on how to use entangled photons from GaAs/AlGaAs quantum dots to transfer information from one node of a network, namely a quantum repeater, to another by proposing an experiment called remote quantum teleportation
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