32,278 research outputs found

    A multiphase-field model for simulating the hydrogen-induced multi-spot corrosion on the surface of polycrystalline metals: Application to uranium metal

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    Hydrogen-induced multi-spot corrosion on the surface of polycrystalline rare metals is a complex process, which involves the interactions between phases (metal, hydride and oxide), grain orientations, grain boundaries, and corrosion spots. To accurately simulate this process and comprehend the underlying physics, a theoretical method is required that includes the following mechanisms: i) hydrogen diffusion, ii) phase transformation, iii) elastic interactions between phases, especially, the interactions between the oxide film and the hydride, iv) elastic interactions between grains, and v) interactions between hydrogen solutes and grain boundaries. In this study, we report a multiphase-field model that incorporates all these requirements, and conduct a comprehensive study of hydrogen-induced spot corrosion on the uranium metal surface, including the investigation of the oxide film, multi-spot corrosion, grain orientation, and grain boundary in the monocrystal, bicrystal, and polycrystal systems. The results indicate that the oxide film can inhibit the growth of hydrides and plays a crucial role in determining the correct morphology of the hydride at the triple junction of phases. The elastic interaction between multiple corrosion spots causes the merging of corrosion spots and promotes the growth of hydrides. The introduction of grain orientations and grain boundaries results in a variety of intriguing intracrystalline and intergranular hydride morphologies. The model presented here is generally applicable to the hydrogen-induced multi-spot corrosion on any rare metal surface.Comment: 22 pages (text), 16 figures (text), 2 table (text), 8 pages (SI), 12 figures (SI

    The Currency of the Anthropocene. Dismantling the Theological Presupposition of Neoliberalism in Kim Stanley Robinson’s The Ministry for the Future

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    This essay analyzes Kim Stanley Robinson’s latest Sci-fi novel, The Ministry for the Future (2020), by focusing on key narrative elements developed in the text that offer solutions to our current climate crisis. Although fictional, these ideas are theoretically relevant because they challenge the current symbolic system of neoliberalism based on a sacrificial economy and a notion of transcendence that demands the infinite accumulation of surplus value. In particular, I examine the import of Robinson’s argument regarding the need for political representation of future generations through the creation of an ad hoc intragovernmental branch (the above-mentioned Ministry of the title of his novel) and a new understanding of value based on the concept of the Carbon Coin reward system

    Can I Get a Witness?—Living While Black Death is Trending

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    It is not uncommon for graphic scenes of violence and death to infiltrate our timelinesfrom retweets, reposts, and shares. I often question how much control do we really have over the images that enter our feed? In what ways are we affected and influenced by these images? How do we relate to these images and video clips that are played and replayed before us? In what ways are these images evoking or are related to past scenes of racist violence? In what ways are these racially violent moments captured in photos and videos and shared online speaking to a Black consciousness? This project comparatively researches and examines the relationship between past modes and methods of Black trauma curation in the past, to contemporary modes of dissemination on social media in order to argue that contemporary uses of spaces such as Instagram, Facebook, and Twitter serve as an extension of previous scrapbooking methods. By comparing The Emmet Till Generation and their curation of trauma via scrapbooks which were used to galvanize social movements, and impact organizing efforts of the youth, The Trayvon Generation today uses social media in a similar fashion; to bear witness, to organize, and to curate digital memorials for the dead. Witnessing is further extended and complicated on digital platforms, providing an abundance of visual evidence that has proven to be vital in leading tp prosecutions and arrests of violent state officials, and perpetrators of extrajudicial violence. These live or recorded moments of witnessing are used not only as evidence, but to inform the public. However, we have always known that it’s always happening somewhere, even if we aren’t around to witness it. With that said, what are the effects of having the duty, and the responsibility to bear witness? Paying particular attention to Black youth, this project examines their presence and usage of social media spaces. By analyzing young Black people’s use of social media platforms in relation to Darnella Frazier’s strategic use Facebook, this project examines how Black youth and witnessing is currently driving a cultural shift in entertainment media that highlights witnessing death as a significant milestone for Black youth that marks the transition between childhood and adulthood. It is also impacting entertainment media that is not marketed towards Black people, further highlighting Black witnessing of racialized violence at the intersection of technology as both a contemporary and future issue through its inclusion in contemporary media.Witnessing for Black people is framed as being both necessary and traumatic. This project concludes with an in depth examination of speculative media to reveal the implications of both the present and the future intersections of race relations, state violence and technology. Through analyses of interviews, image circulation and dissemination, magazine articles, social media platforms, visual and speculative media, this dissertation works to address and attempts to answer the aforementioned questions

    Expanding the Operating Envelopes of Advanced Reactors with Multi-Metallic Layered Composite Materials

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    Current nuclear fuel cladding and structural materials struggle to survive the combined effects of temperature, stresses, and corrosion found in advanced reactor cores, and the development of new materials is expensive and time consuming. An attractive, low-cost, near-term solution is the multi-metallic layered composite (MMLC) material, a material design concept where the tasks of structural integrity and corrosion resistance are assigned to separate material layers. In this work, the operating envelopes of multiple advanced reactor design concepts are computationally analyzed and potentially expanded through the implementation of MMLC fuel cladding materials. First, reactor operating envelopes, defined as the set of neutronic, thermal-hydraulic, and thermo-mechanical reactor core conditions, are identified with two computational tools: the SERPENT Monte Carlo neutron transport code for neutronic analyses, and the REX code for coupled thermal-hydraulic/thermomechanical analyses. REX, a provisionally patented reactor design tool developed specifically for this work, performs a sequence of core subchannel calculations, in which, fuel pin geometries are iteratively modified to force prohibitive thermal and fuel-clad contact stresses in precursory cladding materials. It then quantifies the thermo-mechanical response of MMLC fuel-clad materials with initially-limiting geometries as a function of corrosion-resistant layer width. The calculation sequence concludes with a thermal-hydraulic operating envelope expansion sequence, in which, the MMLCs that expand the reactor thermomechanical performance are tested at elevated coolant temperatures. The results of this work are quantified thermal-hydraulic and thermo-mechanical performance gains in lead-cooled and fluoride salt-cooled designs with MMLC fuel-cladding materials. A base thermo-mechanical design standpoint is determined for a sodium-cooled reactor core whose functional MMLC has yet to be identified. Finally, thermal-hydraulic performance gains for the intermediate heat exchanger of a compact fusion device are determined with a simplified version of the REX framework.Ph.D

    Tuning the electronic properties and redox chemistry of late transition metal and f-element molecular compounds using weak-field ligands

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    This thesis focuses on the use of weak-field ligands as a synthetic tool to access molecular tetravalent lanthanide compounds that can be studied spectroscopically and electrochemically to address broader questions pertinent to better understanding the electronic phenomena observed in bulk f-element materials. First, two different iterations of a tris(diakylamido)imidophosphorane ligand were used to create saddled tetranuclear Cu(I) and Ag(I) clusters. One of the Ag(I) clusters was shown to react with a neutral homoleptic Ce(III) compound and cerium metal shavings to produce the monometallic Ce(IV) imidophosphorane product. The latter example marks the first instance of an oxidative transmetallation reaction between a bulk lanthanide metal with a reagent that exclusively produces a single well-defined molecular tetravalent lanthanide oxidation product. Next, a new ligand type of guanidinate ligand, supported by a tris(diakylamido)imidophosphorane moeitywas used to produce a neutral tris-homoleptic Ce(III) complex that was oxidized to produce a cationic tris-homoleptic Ce(IV) complex. Both compounds were studied electrochemically and spectroscopically. The Ce(IV) compound displayed a Epc of -1.98 V (vs. Fc0/+) in THF, which is more than 1 V more negative than that of other homoleptic cerium guanidinate complexes with a dialkylamido backbone. The pseudo-Voigt fit of the Ce L3-edge XANES spectrum of the tetravalent cerium compound resulted in a nf value of 0.50(2), which is lower than that of many compounds supported by other ligands in the literature. Finally, the tris(piperidinyl)imidophosphorane ligand, [NP(pip)3]1- , was used to build low-coordinate bimetallic Fe(II) and Co(II) molecular clusters with facially exposed metal-metal bonds. Both compounds were exposed to N2O, S8, and Se0, however, the Co(II) bimetallic complex did not react with any of these small molecules. The Fe(II) bimetallic complex reacted with N2O under mild conditions to produce a O2--bridged product and reacted with S8 and Se0 to produce isostructural S22- and Se22- products. The oxidation product, [Fe2(mu2-O)(mu2-NP(pip)3)2(NP(pip)3)2], is structurally unique as it possesses an uncommonly short Fe(III)-Fe(III) distance.Ph.D

    Der Karlsruher Physikkurs für die Sekundarstufe I, Gesamtband

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    Der Karlsruher Physikkurs ist ein Lehrbuch für die Sekundarstufe des Gymnasiums: 3 Bände für die Sek I und 5 Bände für die Sek II. Ihm liegt eine einheitliche Sachstruktur zu Grunde. Er ist dadurch leicht verständlich und gleichzeitig kompakt. Außerdem werden Barrieren zu Nachbardisziplinen abgebaut. Veraltete Konzepte wurden eliminiert, die Zahl der Fachausdrücke stark reduziert. Er wird gern gelesen von Jungen und Mädchen

    Komplexierung von Actiniden in unterschiedlichen Oxidationsstufen mit Hilfe organischer N-Donor Liganden

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    Auch wenn die Actinide Thorium und Uran nunmehr seit ca. 200 Jahren und das erste Transuran-Element seit über 80 Jahren bekannt sind, ist deren chemisches Verhalten noch immer nicht vollständig aufgeklärt. Aufgrund dessen soll die vorliegende Arbeit einen Beitrag zur Aufklärung der Koordinationschemie der Actinide, vor allem der Transurane Neptunium und Plutonium, mit organischen Stickstoff-Donor Liganden leisten und damit zum Schließen bestehender Wissenslücken beitragen. Für die Erreichung dieses Ziels erfolgte die Synthese von neuartigen Actinid-Komplexverbindungen mit Thorium, Uran, Neptunium und Plutonium in den umweltrelevanten Oxidationsstufen +IV bis +VI. Dabei war vor allem der tetravalente Oxidationszustand aufgrund seiner Stabilität bzgl. der frühen Actinide (Th-Pu) unter reduzierenden Bedingungen von Interesse. Neben der Synthese erfolgte die Charakterisierung der Komplexe im Festkörper und in Lösung, um zusammen mit detaillierten quantenchemischen Rechnungen ihre elektronische Struktur und Bindungseigenschaften zu evaluieren. Besonderer Fokus lag dabei auf der Frage, ob und in welchem Ausmaß die 5f-Elektronen an der Bindung zwischen Actinid und Stickstoff-Donor Liganden sowie der Ausbildung eines kovalenten Bindungscharakters beteiligt sind.:1 Motivation und Aufgabenstellung 1 2 Grundlagen 7 2.1 Die Actinide 7 2.1.1 Allgemeines 7 2.1.2 Elektronenstruktur und Oxidationsstufen 8 2.2 SCHIFF´sche Basen als N,O- oder N,N-Donor Liganden 10 2.2.1 Salen, Salenderivate und deren Actinid-Komplexe 10 2.2.2 Pyrrol-basierte SCHIFF´sche Basen und ihre Metall-Komplexe 13 2.3 Actinidkomplexe mit Amido- und Imido-Liganden 17 2.4 Methoden 19 2.4.1 Einkristallröntgendiffraktometrie 19 2.4.2 NMR Spektroskopie 20 2.4.3 HERFD-XANES Spektroskopie 24 2.4.4 Quantenchemische Methoden 25 3 Ergebnisse und Diskussion 31 3.1 Tetravalente Bis-pyren und -pyrophen Komplexe 32 3.1.1 Synthese 32 3.1.2 Untersuchungen im Festkörper 33 3.1.3 Quantenchemische Berechnungen 39 3.1.4 Untersuchung in Lösung 45 3.1.5 Vergleich zu verwandten N,O Donoren des Salen-Typs 51 3.1.6 HERFD-XANES Messungen 63 3.2 Einfluss der Ligandsubstitution bzw. -addition auf die elektronische Struktur der pyren und pyrophen Komplexe 65 3.2.1 Substitution eines pyren Liganden 65 3.2.1 Pyrophen Solvatkomplexe 71 3.3 Hexavalente Uranyl-Komplexe 76 3.3.1 Synthese 76 3.3.2 Festkörperstrukturen und quantenchemische Berechnungen 77 3.3.3 Charakterisierung in Lösung 82 3.4 Die elektronische Struktur eines U(IV)-Amido und U(V)-Imido Komplexes 89 3.4.1 Synthese und Festkörperuntersuchungen 89 3.4.2 Quantenchemische Berechnungen und Einordnung der Effekte 94 4 Fazit und Ausblick 99 5 Experimentelles 103 5.1 Geräte und Methoden 103 5.2 Chemikalien 108 5.3 Synthesen 108 5.3.1 Liganden 109 5.3.2 Deprotonierte Liganden 110 5.3.3 Tetravalente Metallkomplexe mit Pyrrol-basierten Liganden 110 5.3.4 Hexavalente Metallkomplexe mit Pyrrol-basierten Liganden 115 5.3.5 U(IV)-Amido und U(V)-Imido Komplexe 116 6 Literaturverzeichnis 117 7 Anhang 127 7.1 Quantenchemische Berechnungen 127 7.2 SC-XRD 129 7.3 HERFD XANES Messungen 141 7.4 NMR Spektroskopie 142 7.5 IR Spektren 159 7.6 UV-Vis Spektren 161 7.7 Cyclovoltammetrie 163 7.8 Elektronenspray-Ionisation Massensprektrometrie 164 8 Eidesstattliche Erklärung 16

    Construction of radon chamber to expose active and passive detectors

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    In this research and development, we present the design and manufacture of a radon chamber (PUCP radon chamber), a necessary tool for the calibration of passive detectors, verification of the operation of active radon monitors as well as diffusion chamber calibration used in radon measurements in air, and soils. The first chapter is an introduction to describe radon gas and national levels of radon concentration given by many organizations. Parameters that influence the calibration factor of the LR 115 type 2 film detector are studied, such as the energy window, critical angle, and effective volumes. Those are strongly related to the etching processes and counting of tracks all seen from a semi-empirical approach studied in the second chapter. The third chapter presents a review of some radon chambers that have been reported in the literature, based on their size and mode of operation as well as the radon source they use. The design and construction of the radon chamber are presented, use of uranium ore (autunite) as a chamber source is also discussed. In chapter fourth, radon chamber characterization is presented through leakage lambda, homogeneity of radon concentration, regimes-operation modes, and the saturation concentrations that can be reached. Procedures and methodology used in this work are contained in the fifth chapter and also some uses and applications of the PUCP radon chamber are presented; the calibration of cylindrical metallic diffusion chamber based on CR-39 chips detectors taking into account overlapping effect; transmission factors of gaps and pinhole for the same diffusion chambers are determined; permeability of glass fiber filter for 222Rn is obtained after reach equilibrium through Ramachandran model and taking into account a partition function as the rate of track density. The results of this research have been published in indexed journals. Finally, the conclusion and recommendations that reflect the fulfillment aims of this thesis are presented

    Оценка применимости метода масс-спектрометрии с индуктивно связанной плазмой для задач специального индивидуального дозиметрического контроля

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    In the condition of modern radiation hazardous production, higher levels of personnel internal exposure are mainly due to the intake of radionuclides in situations caused by faulty equipment or wrong actions of personnel which can or do result in the exposure that exceeds established standards. In such cases, to determine the intake and committed effective dose, daily amount of urine and/or feces is collected followed by the preparation of loads and their subsequent measurements. For a total, it takes three to eight days to obtain the result depending on the method of measurement used. In case of acute intake of plutonium, it is important to estimate the levels of the nuclide intake as soon as possible in order to decide on treatment strategy and dose reduction. To achieve the above goal, the Southern Urals Biophysics Institute has developed a technique for measuring the plutonium-239 activity in blood using an inductively coupled plasma mass spectrometer as in the first hours and 24 hours after intake (through inhalation or damaged skin) the radionuclide concentration in blood is at its maximum level. Also a method has been developed to measure plutonium in urine aliquot using mass-spectrometry to perform special individual dosimetry monitoring that requires almost no sample preparation which allows to estimate the intake within a few hours. It is shown that, depending on the route of intake and chemical form of plutonium compounds entered, the measurement of plutonium activity in blood and urine aliquot performed by the inductively coupled plasma mass spectrometer method allows to determine from 0.1 to 47% of intake limit within the first 24 hours after an accident. The analysis of a blood sample takes one to one-and-a-half workdays against a week required to analyze a urine sample using alpha-spectrometry. The application of the developed methodology, apart from the goal of individual dosimetry monitoring, will provide new information on the effects of chelation therapy on the plutonium behavior in the human body. В условиях современного радиационно опасного производства повышенные уровни внутреннего облучения персонала обусловлены в основном поступлением радионуклидов в ситуациях, вызванных неисправностью оборудования или неправильными действиями персонала, что может приводить или приводит к облучению выше установленных норм. В таких случаях для определения величины поступления и оценки ожидаемой эффективной дозы внутреннего облучения собирается суточное количество мочи и/или кала, далее следует подготовка счетных образцов и их последующее измерение. В совокупности продолжительность получения результата составляет от 3 до 8 дней в зависимости от метода измерения. В случае острого поступления плутония важно как можно быстрее оценить уровни поступления нуклида в организм, чтобы принять решение о тактике лечения и снижения дозовых нагрузок. Для достижения вышеуказанной цели в Южно-Уральском институте биофизики была разработана методика измерения активности плутония-239 в крови с применением масс-спектрометра с индуктивно связанной плазмой, так как в первые часы и сутки после поступления (ингаляционного или через поврежденные кожные покровы) концентрация радионуклида в крови находится на максимальном уровне. Также разработан метод измерения плутония в аликвоте мочи с использованием масс-спектрометра для выполнения специального индивидуального дозиметрического контроля, практически не требующий пробоподготовки, что позволяет получить оценку поступления в течение нескольких часов. Показано, что в зависимости от пути поступления и химической формы поступающих соединений плутония измерение активности плутония в крови и аликвоте мочи методом масс-спектрометрии с индуктивно связанной плазмой позволяет определять от 0,1 до 47% от предела поступления в течение первых суток после события. Анализ пробы крови занимает от 1 до 1,5 рабочих дней против недели для анализа пробы мочи альфа-спектрометрическим методом. Применение разработанной методики, помимо целей индивидуального дозиметрического контроля, позволит получить новую информацию о влиянии хелатотерапии на поведение плутония в организме человека.

    Key nuclear data for non-LWR reactivity analysis

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    An assessment of nuclear data performance for non-light-water reactor (non-LWR) reactivity calculations was performed at Oak Ridge National Laboratory that involved a thorough literature review to collect related observations made across different research institutions, an interrogation of the latest ENDF/B evaluated nuclear data libraries, and propagation of nuclear data uncertainties to key figures of merit associated with reactor safety for six non-LWR benchmarks. The outcome of this comprehensive study was published in a technical report issued by the US Nuclear Regulatory Commission. This paper provides a summary of the study’s key observations and conclusions and demonstrates with two examples how the various methods available in the SCALE code system were used to identify key cross section uncertainties for non-LWR reactivity analyses