<p>Humans are exposed to metals and metal-containing materials daily, either conscious, e.g. using metal tools or objects, or unconscious, e.g. during exposure to airborne metal-, and metal-containing particles. The diffuse dispersion of metals from different sources in the society, and the concern related to its potential risk for adverse effects on humans have gained an increased public and governmental attention both on a national and international level. In this context, the knowledge on metal release from metallic objects or metal-containing particles is essential for health risk assessment.</p><p>This thesis focuses on the study of metal release from powder particles of stainless steel and Cu-based materials exposed to synthetic body fluids mainly for simulating lung-like environments. The study comprises: i) development of a suitable experimental method for metal release studies of micron sized particles, ii) metal release data of individual alloy constituents from stainless steel powder particles of different particle sizes, and iii) Cu release from different Cu-based powder particles. In addition, the influence of chemical and physical properties of metallic particles and the test media are investigated. Selected results from Ni powder particles exposed to artificial sweat are presented for comparison. The outcome of this research is summarized through ten questions that are formulated to improve the general understanding of corrosion-induced metal release from metallic particles from a health risk perspective.</p><p>A robust, reproducible, fairly simple, and straightforward experimental procedure was elaborated for metal release studies on particles of micron or submicron size. Results in terms of metal release rates show, for stainless steel powder particles, generally very low metal release rates due to a protective surface oxide film, and Fe preferentially released compared to Cr and Ni. Metal release rates are time-dependent for both stainless steel powder particles and the different Cu-containing powders investigated. The release of Cu from the Cu-containing particles depends on the chemical and compositional properties of the Cu-based material, being either corrosion-induced or chemically dissolved. Moreover, the test medium also influences the metal release process. The metal release rate increases generally with decreasing pH of the test media. However, even at a comparable pH, the release rate may be different due to differences in the interaction between the particle surface and specific media.</p><p>The nature of particles is essentially different compared to massive sheet in terms of physical shape, surface composition and morphology. The surface area, and even the surface composition of metallic particles, depend on the particle size. The specific surface area of particles, area per mass, is intimately related to the particle size and has a large effect on the metal release process. Release rates increase with decreasing particle size due to a larger active surface area that takes part in the corrosion/dissolution process. The surface area that actually is active in the corrosion and metal release process (the effective area) governs the metal release process for both particles and massive sheet of metals or alloys. For particles, the effective surface area depends also on agglomeration conditions of particles during exposure.</p>
Identification de caractéristiques réduites pour l'évaluation des performances des systèmes solaires combinés / Identification of restricted characteristics for the evaluation of solar combisystems performanceLeconte, Antoine 14 October 2011 (has links)
Les Systèmes Solaires Combinés (SSC), qui répondent aux besoins d'Eau Chaude Sanitaire (ECS) et de chauffage d'un bâtiment, peuvent réaliser des économies d'énergie conséquentes. Cependant, leurs performances dépendent énormément de leur conception, de leur installation et surtout de l'environnement énergétique auquel ils sont confrontés (c'est-à-dire les besoins thermiques du bâtiment et les ressources solaire). A ce jour, il est impossible de prédire l'économie d'énergie qu'un SSC permettrait de réaliser. Il n'existe aucun test normatif permettant la caractérisation des performances des SSC, ce qui pénalise le développement de son marché. La méthode SCSPT (Short Cycle System Performance Test) a pour objectif d'évaluer les performances annuelles des SSC à partir d'un test de 12 jours sur banc d'essai thermique semi-virtuel. Sa particularité est de considérer chaque système comme un unique ensemble ce qui permet, contrairement aux méthodes de type « composant », de prendre en compte les vraies interactions entre les éléments des SSC lors de leur test. Elle montre de très bons résultats mais ceux-ci sont limités à la prédiction des performances du système pour le seul environnement énergétique adopté lors du test. Ces travaux de recherche proposent une amélioration de la procédure SCSPT en lui ajoutant une étape d'identification d'un modèle générique de SSC à partir de données expérimentales. De cette manière, le modèle identifié pourrait simuler le comportement du SSC testé sur différentes séquences annuelles pour n'importe quel environnement énergétique et ainsi caractériser ses performances (à l'aide de la méthode FSC par exemple). L'architecture proposée pour ce modèle est du type « Boite Grise ». Elle mêle une partie « Boite Blanche » composée d'équations physiques caractéristiques de certains éléments du SSC et une partie « Boite Noire » constituée principalement d'un réseau de neurones artificiels. Une procédure complète est conçue pour entrainer et sélectionner un modèle correspondant aux SSC à partir des données de leur test sur banc d'essai semi-virtuel. Cette approche a été validée numériquement grâce à des simulations de trois modèles détaillés de SSC sous TRNSYS. En comparant leurs résultats annuels avec ceux des modèles « Boites Grises » entrainés à partir d'une séquence 12 jours, ces derniers sont capables de prédire la consommation en énergie d'appoint de manière très précise pour 27 environnements énergétiques différents. L'application concrète de cette nouvelle procédure a été réalisée expérimentalement sur deux SSC réels. Elle a confirmé que l'approche était pertinente et cohérente. Elle a également permis d'identifier quelques améliorations pour que la méthode soit totalement opérationnelle. Ce travaux offrent une base pour avancer dans l'élaboration d'une méthode complète et fiable de caractérisation des SSC qui pourraient conduire à une nouvelle procédure de normalisation (et d'envisager un étiquetage énergétique des SSC. / Solar Combi Systems (SCS) can be very efficient at reducing heat energy bill of a house but their performances depend on the environment they are working in (type of climate and thermal quality of the building). Currently it is impossible to predict how much energy a SCS would save before its installation. There is no standard test to characterize SCS performances and this curbs its market development. The Short Cycle System Performance Test (SCSPT), that is being developed at the French National Institute of Solar Energy (INES, Chambery, France), aims to evaluate SCS annual performance from a test on a semi-virtual test bench. Its special feature is to test the whole system as only one part, unlike “component testing” which can't consider real interaction between combisystems components. The SCSPT method shows good results but performance prediction is limited to only one environment (i.e. one set of system sizing, type of climate and building thermal quality, corresponding with the test). This work proposes an improvement of the SCSPT procedure by identifying a global SCS model from the test data. In this way, the identified model would be able to simulate the tested SCS behaviour in any environment and thus to characterize its performances. The proposed model to identify is a “grey box” model, mixing a “white box” model composed of known physical equations and a “black box” model, which is an Artificial Neural Network (ANN). A complete process is developed to train and select a relevant global SCS model from such a test on semi-virtual test bench. This approach has been validated through numerical simulations of three detailed SCS models. Compared to their annual results, “grey box” SCS models trained from a twelve days sequence are able to predict energy consumption with a good precision for 27 different environments. Concrete experimentations of this procedure have been applied to two real systems. They have confirmed that the approach is pertinent and revealed some points to improve in order to get it totally operational. This work offers major basis to get ahead with a complete method to characterize SCS that could lead to develop a standardization method from performance evaluation (and eventually complete the European norm EN 15316 for instance) and to plan a combisystems performance labelling.
Humans are exposed to metals and metal-containing materials daily, either conscious, e.g. using metal tools or objects, or unconscious, e.g. during exposure to airborne metal-, and metal-containing particles. The diffuse dispersion of metals from different sources in the society, and the concern related to its potential risk for adverse effects on humans have gained an increased public and governmental attention both on a national and international level. In this context, the knowledge on metal release from metallic objects or metal-containing particles is essential for health risk assessment. This thesis focuses on the study of metal release from powder particles of stainless steel and Cu-based materials exposed to synthetic body fluids mainly for simulating lung-like environments. The study comprises: i) development of a suitable experimental method for metal release studies of micron sized particles, ii) metal release data of individual alloy constituents from stainless steel powder particles of different particle sizes, and iii) Cu release from different Cu-based powder particles. In addition, the influence of chemical and physical properties of metallic particles and the test media are investigated. Selected results from Ni powder particles exposed to artificial sweat are presented for comparison. The outcome of this research is summarized through ten questions that are formulated to improve the general understanding of corrosion-induced metal release from metallic particles from a health risk perspective. A robust, reproducible, fairly simple, and straightforward experimental procedure was elaborated for metal release studies on particles of micron or submicron size. Results in terms of metal release rates show, for stainless steel powder particles, generally very low metal release rates due to a protective surface oxide film, and Fe preferentially released compared to Cr and Ni. Metal release rates are time-dependent for both stainless steel powder particles and the different Cu-containing powders investigated. The release of Cu from the Cu-containing particles depends on the chemical and compositional properties of the Cu-based material, being either corrosion-induced or chemically dissolved. Moreover, the test medium also influences the metal release process. The metal release rate increases generally with decreasing pH of the test media. However, even at a comparable pH, the release rate may be different due to differences in the interaction between the particle surface and specific media. The nature of particles is essentially different compared to massive sheet in terms of physical shape, surface composition and morphology. The surface area, and even the surface composition of metallic particles, depend on the particle size. The specific surface area of particles, area per mass, is intimately related to the particle size and has a large effect on the metal release process. Release rates increase with decreasing particle size due to a larger active surface area that takes part in the corrosion/dissolution process. The surface area that actually is active in the corrosion and metal release process (the effective area) governs the metal release process for both particles and massive sheet of metals or alloys. For particles, the effective surface area depends also on agglomeration conditions of particles during exposure. / QC 20101119
Poff, Evan D.
02 June 2022
A method for measuring system-on-a-chip (SoC) cache upsets is presented and evaluated. In contrast to methods that predict cache contents through analysis or memory access patterns, this method uses system registers to read cache memories directly, thereby creating and checking golden copies to detect individual memory upsets during operation. The test method is driven by the device under test itself and does not require a user to set or know a priori the cache contents. A bare-metal implementation of this “direct golden method” on a Zynq UltraScale+ MPSoC logged upsets in the device’s data cache, data tag, and TLB RAM memories during a neutron radiation beam test. For each of these memories, this direct golden method yields cache upset bit cross sections, such as 7.115 × 10^−16 cm^2 for the data cache. Confidence intervals for these bit cross sections overlap such intervals for three other methods, supporting this method’s validity and candidacy for future use.
Four beam-bond test specimens, two in accordance with RILEM TC-RC5 recommendation, labelled as RILEM and two based on a modified form of the ACI 208 beam-bond test method, labelled as Notched, were tested in four-point bending to investigate the bond stress distribution and values along the bar embedment length of a 15 𝑚𝑚 nominal diameter GFRP rebar. The beams experienced failure through the rupturing of the longitudinal GFRP tensile reinforcement. In addition, two Modified and ten Standard pullout specimens were tested using the same bar. The beam-bond and the Modified pullout specimens had embedment length of 600 𝑚𝑚 while the Standard pullout specimens had, in accordance with CSA S806, 60 𝑚𝑚 embedment, or four times the bar nominal diameter. The first Modified pullout specimen experienced concrete splitting failure and as a result, the second was lightly confined and failed by GFRP bar rupture. All ten Standard pullout specimens failed due to bar pullout. It was determined that the actual bond stress distribution as a function of the embedment length is practically parabolic and can be described by the derivative of a modified form of the logistic growth function used to approximate the strain distribution along the embedment length. Furthermore, the maximum bond stress location progressively moves from the loaded-end towards the unloaded-end as the bond continues to deteriorate with increasing GFRP stress levels. The development length recommendations by ACI 440.1 and to a lesser degree, CSA S806 and CSA S6 are quite conservative compared to that which is required. It is observed that pullout tests alone cannot provide sufficient knowledge regarding the bond behaviour of FRP reinforcement; consequently, the results of beam-bond testing are more appropriate. Standard pullout tests may be incorporated into quality assurance programs with the understanding that they cannot provide valuable information regarding bond stress distribution and required development length in real structural elements with large embedment lengths. In terms of the beam-bond test method, the RILEM TC-RC5 design recommendation appears to be superior since it eschews severe stress perturbation caused by incidence of flexural cracks at beam midspan. As a result, it produces stability in the terms of the data gathered from the strain gauges placed on the GFRP bar. This benefit outweighs the ease of constructability of the Notched beams as well as their resemblance to real beams. / Thesis / Master of Applied Science (MASc) / The force that bonds a reinforcing rod to concrete is determined using three test methods. Each method is recommended by some design standards, but it is unclear how the results of these tests compare to each other. To shed light on the issue, a 15 𝑚𝑚 fibre glass rod was tested using three well-known test methods. It was discovered that two of the methods give results that are reasonably close while the third gives variable results that generally do not agree with the results of the other two. It was also discovered that the required embedment length recommended for such a bar by design codes and standards are relatively excessive because they underestimate the actual bond strength of the rod. Since sometimes it may be difficult to provide such long length in practice, it is recommended that the code requirements be revisited.
試題預覽對國中生英語聽力表現之影嚮：個案研究 / The Effects of Test Question Preview on Junior High School Students' English Listening Comprehension: a Case Study陳淑菁, Chen,Shu-ching Unknown Date (has links)
本研究主要探討四方面。第一、探討試題預覽是否有助於聽力成績表現。第二、進一步探究試題預覽的效益是否因聽力程度不同而有所差異。第三、了解學生以試題預覽方式參加聽力測驗的實際經驗與看法。第四、研究試題預覽是否是一個可行的評量聽力的測驗方式。 參加本實驗的受試者為來自竹山國中120位三年級的學生。首先，他們被分為能力相當的兩組，每一組再被細分為高、中、低三個能力組別，接著研究者分別對兩組受試者施以聽力測驗，不同之處在於實驗組提供試題預覽。最後，實驗組的受試者須填寫一份關於他們對此測驗方式 (試題預覽方式) 的經驗及觀感。 本研究之主要發現如下: 1. 受試者在聽力測驗中顯著受益於試題預覽。 2. 高、中程度的受試者比低程度的受試者從試題預覽中獲得較多的助益。 3. 由問卷統計結果得知大部分受試者對於試題預覽表達正面的態度。 4. 試題預覽促進聽者預測聽力內容及使用由上而下的聽力理解方式是一個可行的評量聽力的測驗方式。 最後, 本研究建議老師們在實施聽力測驗時應以試題預覽的方式進行。再者, 老師們可以以試題預覽做為訓練聽力時的教學活動。另外, 老師們必須考慮學生聽力程度的不同並為低程度者設計額外的聽力訓練活動以便提升其聽力理解能力。 / The present study chiefly focuses on four issues. The first issue concerns whether test question preview method can make test takers get better scores on listening comprehension tests or not. The second issue examines whether the effectiveness of test question preview varies with the students’ proficiency levels or not. The third issue aims to probe test takers’ practical experience of taking the listening comprehension test with question preview test method. The fourth issue explores if question preview method is practical in measuring the students’ listening comprehension. The participants of this study were 120 third-year students at Chu-shan Junior High School. Firstly, they were divided into two homogeneous groups, each group were further subdivided into three subgroups- high, medium and low proficiency. Then the researcher administered the experimental test to both the experimental group and the control group; the only difference in the treatment was that question preview was used to the experimental group. At last, the experimental group was asked to fill in a questionnaire designed to investigate the experience of taking the listening test with test question preview method. The major findings of the study are as follows: (1)The junior high EFL students benefited significantly from the test question preview. (2)Listeners of high and medium proficiency level gained much assistance from the question preview than those of low proficiency level. (3)Questionnaire responses confirmed the positive effects of the test question preview. (4)The test question preview promoted information prediction and top-down information processing of test takers; therefore, it is a practical method for assessing learners’ listening comprehension. Therefore, it is suggested that teachers incorporate question preview method in the tests of listening comprehension. In addition, it is necessary for teachers to use question previewing as a teaching activity when training students’ listening skills. Finally, teachers should pay more attention to the differences in students’ listening ability and design some other additional activities for low proficiency listeners to promote their ability of understanding the previewed questions and improve efficiency of listening.
Vandenilio kuro elementų tyrimas srovės trūkio metodu / Investigation of Fuel Cells by Current Interrupt TechniqueTamošaitis, Kęstutis 03 January 2011 (has links)
Bakalauro baigiamąjį darbą „ Vandenilio kuro elementų tyrimas srovės trūkio metodu“ sudaro 5 skyriai: įvadas, teorinė dalis, tyrimų dalis, išvados, literatūra ir priedai. Darbo apimtį sudaro 73 puslapiai, 69 paveikslėliai, 3 lentelės ir 4 priedai. Darbe aprašomos įvairių tipų kuro elementai, jų veikimas. Nagrinėjama PEM kuro elemento veikimo principai. Pateikti PEM kuro elemento savybių eksperimentinio tyrimo rezultatai. / The final work for bachelors degree „Investigation of Fuel Cells by Current Interrupt Technique“ consists of 5 parts: introduction, theoretical part, research part, conclusions, literature and accessories. The work consists of 73 pages, 69 pictures, 3 tables and 4 accessories. This work describes various types of fuel cells, how it works. Operation principles of PEM fuel cell element are analysed. The results of experimental examination of PEM fuell cell element are give.
Evaluation of Canadian unconfined aggregate freeze-thaw tests for identifying nondurable aggregates.Mummaneni, Santosh Kumar January 1900 (has links)
Master of Science / Department of Civil Engineering / Kyle Riding / Concrete is most widely used material in construction industry, which is made up of cement, water and aggregates as its major ingredients. Aggregates contribute to 60 to 75 % of the total volume of concrete. The aggregates play a key role in the concrete durability. The U.S Midwest has many aggregates that can show distress in the field under freezing and thawing conditions. The objective of this research was to determine if the Test Method for the Resistance of Unconfined Coarse Aggregate to Freezing and Thawing, method CSA A23.2-24A, could be used to differentiate good from poor performing aggregates in concrete. In this study fifty one KDOT aggregates (including twelve ledge and thirty nine production samples) were tested for freeze thaw resistance using CSA A23.2-24A test method and were compared to the results of the standard KDOT aggregate qualification tests. In addition to performing the CSA test method using a 3% sodium chloride solution, a subset of the aggregates were tested using either a 3% magnesium chloride or calcium chloride solution to determine the effects of the salt type on the aggregate performance. No correlation was found between the CSA A23.2-24A test method results and the standard KDOT aggregate qualification tests. The results also indicated that the mass loss in the CSA A23.2-24A was similar for the aggregate sizes tested. The use of alternate salt solutions like MgCl2 and CaCl2 resulted in increased freeze thaw mass loss in limestone aggregates.
Método de determinação de resistência à tração e módulo de elasticidade de partículas de agregados graúdos naturais. / Mechanical properties of natural aggregate paricles and their influence on the mechanical behavior of concrete.Silva, Natalia Vieira da 22 February 2018 (has links)
Esse trabalho tem como objetivo estabelecer um método simples de ensaio que permita determinar a resistência à tração e módulo elástico de partículas individuais de agregados graúdos naturais submetidas à carga de compressão. O método de ensaio foi desenvolvido baseado no ensaio de carga pontual (Point Load Test) que permite obter a resistência à tração de partículas. Para a determinação do módulo de elasticidade foi acoplado ao método um LVDT e foi satisfeita a condição para aplicação da teoria de contato de Hertz (contato curvo-plano entre as partículas e as fixações de aplicação da carga). Inicialmente a metodologia foi avaliada utilizando como material de referência partículas de vidro (com geometrias similares aos agregados). Após a validação no vidro, o método de ensaio foi aplicado em agregados graúdos de granito. Propôs-se um método de seleção de partículas com base na sua distribuição de frequência de absorção, com o intuito de reduzir a quantidade de partículas testadas mecanicamente necessárias para obter a distribuição de Weibull da resistência à tração (e módulo de elasticidade). Para tanto, foi feita a determinação da absorção de água individual de centenas de partículas selecionadas por amostragem a esmo da população de agregados. Com base nos resultados, foi possível determinar a distribuição de Weibull da resistência à tração e módulo de elasticidade das partículas. Observou-se que as resistências à tração variaram de 3 a 15 MPa. Os agregados possuíam aproximadamente 10% da população de partículas com resistência à tração inferior a 5 MPa, o que pode influenciar as classes de resistência à compressão de concretos >50MPa. Os módulos elásticos dos agregados também foram variáveis (18-67 GPa) e aproximadamente 10% da população de partículas com módulo elástico <30 GPa. Isso pode limitar o módulo de elasticidade do concreto (que geralmente é em torno de 27 GPa), dependendo do processo de escolha dos agregados. As funções exponenciais inversas fundamentais entre essas propriedades mecânicas e a porosidade foram confirmadas (para valores médios). / The aim of this work is to establish a simple test method to determine the tensile strength and elastic modulus of individual natural aggregate particles subjected to a compression load. The test method was developed based on the Point Load Test, that allows to obtain the tensile strength of particles. For the determination of the elastic modulus, an LVDT was coupled to the method and the condition for application of Hertz contact theory (curved-plane contact between the particles and the load application fixations) was satisfied. Initially, the method was evaluated using glass particles as reference (with geometries similar to aggregates). After validation on the glass, the test method was applied to coarse granite aggregates. A method of particle selection was proposed based on its absorption frequency distribution, in order to reduce the amount of mechanically tested particles required to obtain the Weibull distribution of tensile strength (and elastic modulus). For this purpose, the determination of the individual water absorption of hundreds of particles selected by random sampling of the population of aggregates was made. Based on the results, it was possible to determine the Weibull distribution of the tensile strength and elastic modulus of the particles. The tensile strengths ranged from 3 to 15 MPa. The aggregates had approximately 10% of the particles population with tensile strength less than 5 MPa, which may influence the classes of concrete with compressive strength > 50MPa. The elastic modulus of the aggregates was also variable (18-67 GPa), with approximately 10% of the particle population with elastic modulus <30 GPa. This may limit the elastic modulus of the concrete (usually around 27 GPa) depending on how the aggregates are selected. The fundamental inverse exponential functions between these mechanical properties and the porosity were confirmed (for mean values).
De Caso y Basalo, Francisco Jose
15 December 2010
The development of composite materials by combining two or more constituents with improved mechanical properties, when compared to either of the constituents alone, has existed since biblical times when straw or horse hair was mixed with clay or mud to produce bricks. During the second half of the twentieth century, modern composites known as fiber reinforced polymers (FRP) - consisting of a reinforcing phase (fibers) embedded into a matrix (polymeric resin or binder) - were developed to meet the performance challenges of space exploration and air travel. With time, externally-bonded FRP applications for strengthening of reinforced concrete (RC) structures gained popularity within the construction industry. To date, the confinement of RC columns using FRP systems is a convenient and well established solution to strengthen, repair and retrofit structural concrete members. This technology has become mainstream due to its cost effectiveness, and relative ease and speed of application with respect to alternative rehabilitation techniques such as steel or concrete jackets. However, significant margins exist to advance externally-bonded composite rehabilitation technologies by addressing economic, technological, and environmental issues posed by the use of organic polymer matrices, some of which are addressed in this dissertation. Articulated in three studies, the dissertation investigates the development of a sustainable, reversible, and compatible fiber reinforced cement-based matrix (FRC) composite system for concrete confinement applications in combination with a novel test method aimed at characterizing composites under hydrostatic pressure. Study 1 develops and characterizes a FRC system from different fiber and inorganic matrix combinations, while evaluating the confinement effectiveness in comparison to a conventional FRP system. The feasibility of making the application reversible was investigated by introducing a bond breaker between the concrete substrate and the composite jacket in a series of confined cylinders. The prototype FRC system produced a substantial increase in strength and deformability with respect to unconfined cylinders. A superior deformability was attained without the use of a bond breaker. The predominant failure mode was loss of compatibility due to fiber-matrix separation, which points to the need of improving fiber impregnation to enable a more efficient use of the constituent materials. Additionally semi-empirical linear and nonlinear models for ultimate compressive strength and deformation in FRC-confined concrete are also investigated. Study 2 compares through a life cycle assessment (LCA) method two retrofitting strategies: a conventional organic-based, with the developed inorganic-based composite system presented in Study 1, applied to concrete cylinders by analyzing three life cycle impact indicators: i) Volatile Organic Compound (VOC) emissions, ii) embodied energy, and, iii) carbon foot print. Overall the cement-based composite provides an environmentally-benign alternative over polymer-based composite strengthening system. Results also provide quantitative information regarding the environmental and health impacts to aid with the decision-making process of design when selecting composite strengthening systems. Study 3 is divided into two parts, Part A presents the development of a novel "Investigation of Circumferential-strain Experimental" (ICE) methodology for characterization of circumferential (hoop) strain of composite laminates, while Part B uses the experimental data reported in Part A to explicitly evaluate the effect of FRP jacket curvature and laminate thickness on strain efficiency. Results showed that the proposed ICE methodology is simple, effective and reliable. Additionally, the ultimate circumferential strain values increased with increasing cylinder diameter, while being consistently lower when compared to similar flat coupon specimens under the same conditions. The ultimate FRP tensile strain was found to be a function of the radius of curvature and laminate thickness, for a given fiber ply density and number. The effect of these findings over current design guidelines for FRP confined concrete was also discussed.
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