| 1. |
- Panuzzo, P., et al.
(författare)
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Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry
- 2024
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 686
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Tidskriftsartikel (refereegranskat)abstract
- Context. Gravitational waves from black-hole (BH) merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models-And also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars.Aims. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors.Methods. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions.Results. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70a ±a 0.82aM- BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc.Conclusions. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way.
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| 2. |
- Sumaila, U. Rashid, et al.
(författare)
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WTO must ban harmful fisheries subsidies
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 374:6567, s. 544-544
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- El-Sadek, M.H., et al.
(författare)
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Non-isothermal carbothermic reduction kinetics of mechanically activated ilmenite containing self-reducing mixtures
- 2018
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer. - 1388-6150 .- 1588-2926. ; 131:3, s. 2457-2465
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Tidskriftsartikel (refereegranskat)abstract
- Effect of mechanical activation on carbothermic reduction kinetics and mechanism of ilmenite concentrate containing self-reducing mixture has been investigated using a combination of thermogravimetry and X-ray diffraction. Thermogravimetric comparative study of mechanically activated and non-activated ilmenite concentrate containing self-reducing mixtures with C/O molar ratio of 1.5 was conducted non-isothermally. The samples were heated up to 1573 K at three different heating rates (10, 15, and 20 K min−1) under controlled atmosphere. The reduction mechanism of mechanically activated mixture was followed by X-ray diffraction analysis of arrested samples at different reduction extents. In addition, reaction kinetics was further investigated and corresponding kinetic parameters were estimated using isoconversional (model-free) and model-fitting (Coats–Redfern) methods.
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| 4. |
- Osman, Ahmed M. Shahat, et al.
(författare)
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Big Data Analytics and Smart Cities : A Loose or Tight Couple?
- 2017
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Ingår i: Proceedings of the International Conference on ICT, Society and Human Beings 2017. - : IADIS. - 9789898533678 ; , s. 157-168
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Konferensbidrag (refereegranskat)abstract
- Smart City (SC) is an emerging concept aiming at mitigating the challenges raised due to the continuous urbanization development. To face these challenges, government decision makers sponsor SC projects targeting sustainable economic growth and better quality of life for inhabitants and visitors. Information and Communication Technologies (ICT) is the enabling technology for smartening. These technologies yield massive volumes of data known as Big Data (BD). If spawned BD are integrated and analyzed, both city decision makers and citizens can benefit from valuable insights and information services. The process of extracting information and insights from BD is known as Big Data Analytics (BDA). Although BDA involves non-trivial challenges, it attracted academician and industrialist. Surveying the literature reveals the novelty and increasing interest in addressing BD applications in SCs. Although literature is replete with abundant number of articles about SCs applications harnessing BD, comprehensive discussion on BDA frameworks fitting SCs requirements is still needed. This paper attempts to fill this gap. It is a systematic literature review on BDA frameworks in SCs. In this review, we will try to answer the following research questions: what are the big data analytics frameworks applied in smart cities? what are the functional gaps in the current available frameworks? what are the conceptual guidelines of designing integrated scalable big data analytics frameworks for smart cities purposes? The paper concludes with a proposal for a novel conceptual analytics framework to serve SCs requirements. Additionally, open issues and further research directions are presented.
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| 5. |
- Osman, Ahmed M. Shahat, et al.
(författare)
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Data-Driven Decisions in Smart Cities: A Digital Transformation Case Study
- 2022
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Ingår i: Applied Sciences. - Basel, Switzerland : MDPI. - 2076-3417. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between big data analytics (BDA) and smart cities (SCs) has been addressed in several articles. However, few articles have investigated the influence of exploiting BDA in datadriven decision-making from an empirical perspective in a case study context. Accordingly, we aim to tackle this scarcity of case-study research addressing the interrelationships between SCs, BDA, anddecision-making. Filling this gap will shed light on the challenges and design principles that shouldbe considered in designing a BDA artifact in the domain of smart cities. We analyze a case study of a digital transformation project in Egypt. Results show a tangible positive effect of utilizing dataanalytics in support of the decision-making process.
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| 6. |
- Osman, Ahmed M. Shahat
(författare)
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Smart Cities and Big Data Analytics : A Data-Driven Decision-Making Perspective
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The phenomenon of digitalization has led to the emergence of a new term—big data. Big data refers to the vast volumes of digital data characterized by its volume, velocity, variety, veracity, and value. The accumulation of enormous amounts of digital data has encouraged academics to develop appropriate technologies and algorithms to manage and analyze these data in order to leverage the embedded relationships within the data to support decision-making. This approach has revolutionized the organizational strategies of most business areas by digitally transforming business operations and decision-making processes.A “smart city” is a new concept that depends primarily on digitization and big data analysis. The aim of a smart city is to tackle the challenges of ever-increasing urbanization by utilizing atypical approaches. The utilization of big data analysis in smart cities has been investigated thoroughly in the literature from various aspects, such as those related to recommended technologies and the domains of applications. A smart city is a compound system with multi-domain attributes in which the citizens represent key participants in decision-making. However, harnessing big data analysis to support decision-making in the smart city context is rarely approached in academia. The infrequency of this type of research was sufficient to motivate this interesting research. Two research questions drive this thesis: RQ1: What are the challenges of utilizing big data analytics (BDA) to enable decision-making in smart cities? RQ2: What are the design principles of the BDA framework in the context of smart cities? To address these research questions, numerous research methods were applied, including a systematic literature review, design science research, use case, and case study. In addition, internationally acknowledged information systems databases were searched to collect quality scholarly articles and conference proceedings: ACM Digital Library, IEEE, SCOPUS, Springer Link, INSPEC, INSPEC, and Web of Science. A freely published dataset for experimental purposes on Yelp (www.yelp.com) was used for the use case experiment. Lastly, the case study was based on data from a national Egyptian digital transformation project called Nafeza.The research findings revealed the need to introduce an inventive framework for exploiting big data analysis in smart city applications. The main contribution of this research is the proposal of a novel framework for utilizing big data analytics in smart cities. The proposed framework, the Smart Cities Data Analytics Panel (SCDAP), is a domain-independent big data analysis framework. It compiles the relevant design principles mentioned in the literature, particularly those that are distinctive to smart cities. The design principles of SCDAP are founded on the literature review, use case, and case study methodologies and are the main contribution of this research.As the four papers that formed the foundation of this thesis combine theoretical and practical research, the contributions of this research can be of direct benefit to academic researchers in this field and practitioners of smart city projects.
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| 7. |
- Osman, Ahmed M. Shahat, et al.
(författare)
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Smart Cities and Big Data Analytics: A Data-Driven Decision-Making Use Case
- 2021
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Ingår i: Smart Cities. - Basel, Switzerland : MDPI. - 2624-6511 .- 2624-6511. ; 4:1, s. 286-313
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Tidskriftsartikel (refereegranskat)abstract
- Interest in smart cities (SCs) and big data analytics (BDA) has increased in recent years, revealing the bond between the two fields. An SC is characterized as a complex system of systems involving various stakeholders, from planners to citizens. Within the context of SCs, BDA offers potential as a data-driven decision-making enabler. Although there are abundant articles in the literature addressing BDA as a decision-making enabler in SCs, mainstream research addressing BDA and SCs focuses on either the technical aspects or smartening specific SC domains. A small fraction of these articles addresses the proposition of developing domain-independent BDA frameworks. This paper aims to answer the following research question: how can BDA be used as a data-driven decision-making enabler in SCs? Answering this requires us to also address the traits of domain-independent BDA frameworks in the SC context and the practical considerations in implementing a BDA framework for SCs' decision-making. This paper's main contribution is providing influential design considerations for BDA frameworks based on empirical foundations. These foundations are concluded through a use case of applying a BDA framework in an SC's healthcare setting. The results reveal the ability of the BDA framework to support data-driven decision making in an SC.
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| 8. |
- Zaki, Zaki I., et al.
(författare)
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Combustion synthesis of NbC/ZrO2 composites : Influence of Cr additives on the microstructure and mechanical properties
- 2021
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Ingår i: International Journal of Applied Ceramic Technology. - : John Wiley & Sons. - 1546-542X .- 1744-7402. ; 18:5, s. 1502-1509
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Tidskriftsartikel (refereegranskat)abstract
- Composites of NbC/ZrO2 reinforced with different weight ratios of Cr metal were prepared by dynamic compaction combustion from a blend of Nb2O5-Zr-Cr powders. Factors controlling the synthesis process, the microstructure and the mechanical properties of the samples, such as Cr wt% and the compression loads were studied. The samples were characterized by XRD, SEM, porosity and hardness measurements. The porosity value of sample with no additives was high and reached 31.6 vol%. A sudden decrease in the sample porosity to 2.4 vol % was noticed for sample containing 3.0 wt% of Cr. A high density sample with less than 2.0 vol % porosity and a maximum hardness of 1038 HV was produced using 5.0 wt% Cr under 300 MPa compression load. Detailed thermodynamic calculations for the effect of Cr additives on the physico-chemical properties of the system were introduced.
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| 9. |
- Ahmed, Hesham M., et al.
(författare)
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Dynamic Thermal Diffusivity Measurements - A Tool for Studying Gas-Solid Reactions
- 2011
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Ingår i: DIFFUSION IN SOLIDS AND LIQUIDS VI, PTS 1 AND 2. - Durnten-Zurich : Trans Tech Publications Inc.. ; , s. 217-222, s. 217-222
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Konferensbidrag (refereegranskat)abstract
- In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO(4) has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H(2) gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO(4) and Ni-W, produced by the reduction of NiWO(4) at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.
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| 10. |
- Ahmed, Hesham M., 1981-
(författare)
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Investigations of the Kinetics of Reduction and Reduction/Carburization of NiO-WO3 Precursors.
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Kinetic studies of reduction of the mixtures of NiO and WO3 having different Ni/(Ni+W) molar ratios in flowing hydrogen gas were investigated by means of Thermo Gravimetric Analysis (TGA), Fluidized Bed (FB) technique as well as Thermal diffusivity measurements under isothermal conditions. In the case of TGA, the reaction progress was monitored by mass loss, while evolved gas analysis by a gas chromatograph was the indicator of the reaction progress in the case of FB. The results indicate that the reduction reaction proceeds through three consecutive steps, viz. NiO-WO3 Ni-WO3 Ni-WO2 Ni-W The present results show that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product. During the investigations, it was found that there was a delay in the reaction during the hydrogen reduction of NiO-WO3 mixed oxides in a fluidized bed reactor. In order to understand the same, a theoretical model was developed to estimate the apparent reaction rate constant for the reduction reaction from the intrinsic chemical reaction rate constant. Appropriate differential mass balance equations based on intrinsic chemical reaction rate constants and thermodynamic equilibria were developed. The proposed model was successfully applied in predicting the overall reaction kinetics of a fluidized bed reactor. This model is also suitable for scale-up calculations. SEM images showed that the particle size of the final product was dependent on the Ni/(Ni+W) molar ratio; smaller particles were formed at higher nickel contents. X-ray diffractions of the reduced precursors exhibited slight shift of Ni peaks from the standard one indicating the dissolution of W into Ni. A new method for studying kinetics of the hydrogen reduction of NiO-WO3 precursors was developed in which the reaction progress was monitored by following the change of thermal diffusivity of the precursors. Activation energies of reduction as well as sintering were calculated. This method is considered unique as it provides information regarding the physical changes like sintering, change of porosity and agglomeration along with the chemical changes occurring during the gas/solid reaction. As a continuation of the kinetic studies, Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of Ni-W-O system using H2-CH4 gas mixtures by TGA. The results showed that the reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The above-mentioned experiments were conducted in such a way to ensure that the reaction was controlled by the chemical reaction. The activation energies of the reduction as well as carburization processes at different stages were calculated accordingly. The present dissertation demonstrates the potential of the investigations of gas/solid reactions towards tailoring the process towards materials with optimized properties as for example introduction of interstitials. The present process design is extremely environment-friendly with reduced number of unit processes and the product being H2O.
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