| 1. |
- Aartsen, M. G., et al.
(författare)
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Very high-energy gamma-ray follow-up program using neutrino triggers from IceCube
- 2016
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Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e. g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015.
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| 2. |
- Khayyeri, Hanifeh, et al.
(författare)
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Tissue differentiation in an in vivo bioreactor: in silico investigations of scaffold stiffness
- 2010
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Ingår i: Journal of Materials Science: Materials in Medicine. - : Springer Science and Business Media LLC. - 1573-4838 .- 0957-4530. ; 21:8, s. 2331-2336
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Tidskriftsartikel (refereegranskat)abstract
- Scaffold design remains a main challenge in tissue engineering due to the large number of requirements that need to be met in order to create functional tissues in vivo. Computer simulations of tissue differentiation within scaffolds could serve as a powerful tool in elucidating the design requirements for scaffolds in tissue engineering. In this study, a lattice-based model of a 3D porous scaffold construct derived from micro CT and a mechano-biological simulation of a bone chamber experiment were combined to investigate the effect of scaffold stiffness on tissue differentiation inside the chamber. The results indicate that higher scaffold stiffness, holding pore structure constant, enhances bone formation. This study demonstrates that a lattice approach is very suitable for modelling scaffolds in mechano-biological simulations, since it can accurately represent the micro-porous geometries of scaffolds in a 3D environment and reduce computational costs at the same time.
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| 3. |
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| 4. |
- Lu, Xuekun, et al.
(författare)
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Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography.
- 2019
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 96, s. 400-411
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. STATEMENT OF SIGNIFICANCE: This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.
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| 5. |
- Quack, Niels, et al.
(författare)
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Integrated silicon photonic MEMS
- 2023
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Ingår i: MICROSYSTEMS & NANOENGINEERING. - : Springer Nature. - 2055-7434. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications, including very high data rate optical communications, distance sensing for autonomous vehicles, photonic-accelerated computing, and quantum information processing. The success of silicon photonics has been enabled by the unique combination of performance, high yield, and high-volume capacity that can only be achieved by standardizing manufacturing technology. Today, standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components, including low-loss optical routing, fast modulation, continuous tuning, high-speed germanium photodiodes, and high-efficiency optical and electrical interfaces. However, silicon's relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption, which are substantial impediments for very large-scale integration in silicon photonics. Microelectromechanical systems (MEMS) technology can enhance silicon photonics with building blocks that are compact, low-loss, broadband, fast and require very low power consumption. Here, we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components, with wafer-level sealing for long-term reliability, flip-chip bonding to redistribution interposers, and fibre-array attachment for high port count optical and electrical interfacing. Our experimental demonstration of fundamental silicon photonic MEMS circuit elements, including power couplers, phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications, neuromorphic computing, sensing, programmable photonics, and quantum computing.
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| 6. |
- Caut, Alexander, 1994, et al.
(författare)
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Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits
- 2022
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 40:15, s. 5190-5200
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of angled flip-chip integration of a singlemode 850 nm vertical-cavity surface-emitting laser (VCSEL) on a silicon nitride photonic integrated circuit (PIC) is presented. Using numerical FDTD simulations, we consider the conditions under which the VCSEL can be integrated at an angle over a grating coupler with high coupling efficiency and low optical feedback. With both coupling efficiency and feedback decreasing with increasing angle, there is a trade-off. With co-directional coupling, first-order diffraction loss sets in at a critical angle, which further reduces the coupling efficiency. No such critical angle exists for contra-directional coupling. We also experimentally demonstrate angled flip-chip integration of GaAs-based 850 nm single transverse and polarization mode VCSELs over grating couplers on a silicon-nitride PIC. At the output grating coupler, light is either collected by an optical fiber or converted to a photocurrent using a flip-chip integrated GaAs-based photodetector. The latter forms an on-PIC optical link. We measured an insertion loss of 21.9, 17.6 and 20.1 dB with a singlemode fiber, multimode fiber and photodetector over the output grating coupler, respectively.
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| 7. |
- Florio, B. J., et al.
(författare)
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Mould-taper asymptotics and air gap formation in continuous casting
- 2015
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Ingår i: Applied Mathematics and Computation. - : Elsevier BV. - 0096-3003 .- 1873-5649. ; 268, s. 1122-1139
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Tidskriftsartikel (refereegranskat)abstract
- We develop a coupled thermomechanical model, that includes mould taper, for the formation of air gaps in the vertical continuous casting of round billets. The system is very sensitive to the small width of the air gap. Mould tapers are used to mitigate the contraction of the solidified shell during cooling. We apply numerical and perturbation methods to show that a small mould taper significantly reduces the insulating effect of the air gap. The analysis is presented in a more transparent and less computationally expensive way than earlier, fully numerical models. We also consider a theoretical ideal taper, which eliminates the air gap altogether. The air gap is found to be quite robust; increasing the size of the taper does not constitute an equal reduction in the air gap size. Sample computations are carried out using parameters for the continuous casting of a pure metal (copper), although the framework can easily be extended to the continuous casting of alloys.
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| 8. |
- Florio, B. J., et al.
(författare)
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On the interactive effects of mould taper and superheat on air gaps in continuous casting
- 2017
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Ingår i: Acta Mechanica. - : Springer. - 0001-5970 .- 1619-6937. ; 228:1, s. 233-254
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Tidskriftsartikel (refereegranskat)abstract
- The formation of an air gap in continuous casting systems is detrimental to the process efficiency as it acts to thermally insulate the cast from the water-cooled mould. By tapering the mould wall, the thermal contraction of the cooling cast can be accommodated so that the thickness of the air gap is decreased. We consider a coupled thermomechanical model to investigate the effect of mould tapering on the formation and thickness of the air gap in an axisymmetric mould. Using asymptotic techniques, the model is reduced to allow analytic and inexpensive numerical investigations while maintaining the essential characteristics of the thermomechanical process. This work improves on previous models by including superheat, where the incoming molten metal is at a higher temperature than its melting point. The degree of superheating also affects the formation and thickness of the air gap and presents a viable alternative for control of the system. The efficacy of mould tapering in the presence of superheat is examined.
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| 9. |
- Haglund, Erik, 1985, et al.
(författare)
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High-power single transverse and polarization mode VCSEL for silicon photonics integration
- 2019
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 27:13, s. 18892-18899
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. We demonstrate a 6.5 mW single transverse and polarization mode GaAs-based oxide-confined VCSEL at 850 nm. High power is enabled by a relatively large oxide aperture and an epitaxial design for low resistance, low optical loss, and high slope efficiency VCSELs. With the oxide aperture supporting multiple polarization unrestrained transverse modes, single transverse and polarization mode operation is achieved by a transverse and polarization mode filter etched into the surface of the VCSEL. While the VCSEL is specifically designed for light source integration on a silicon photonic integrated circuit, its performance in terms of power, spectral purity, polarization, and beam properties are of great interest for a large range of applications.
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| 10. |
- Obrien, Eugene J., et al.
(författare)
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Design of Roads in Harmony with Wildlife
- 2016
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Ingår i: Transportation Research Procedia. - : Elsevier BV. - 2352-1465. ; , s. 509-517
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Konferensbidrag (refereegranskat)abstract
- 'Procedures for the Design of Roads in Harmony with Wildlife' or 'Harmony' is a project that aims to develop sustainable solutions to road transport challenges that are in harmony with wildlife. This paper summarises Harmony's work in the areas of Environmental Legislation and Guidelines, Project Appraisal, and Procurement Practices. The project mainly focuses on practices in the eight reference countries of Ireland, the United Kingdom, Belgium, the Netherlands, Hungary, Austria, Sweden and Denmark. A review of Environmental Impact Assessment (EIA) and Appropriate Assessment (AA) is carried out.As part of this review, a database of over 80 Environmental Impact Statements (EIS) and Appropriate Assessment reports is analysed to identify the similarities and differences between countries in the implementation of the duties required by EU Environmental Legislation. It is found that the degree of implementation under the headings considered varies greatly between countries. It is concluded that increased guidance on monitoring be provided in all countries. Project Appraisal for transport infrastructure is the process of assessing whether capital expenditure is justified for a project and ensuring that it is allocated to the best transport solution to achieve the objectives of that project whilst complying with planning policy and national and EU legislation.The project appraisal methodologies used in the reference countries are compared with the aim of identifying a set of tools to enable rational and sensible decisions to be made. The approach used in the UK is recommended for adoption by all Member States. This paper then examines existing approaches to the procurement of road constructions in the reference countries. The different types of contracts used for procurement are described and the benefits and disadvantages of different contract types are discussed.Recommendations are then made as to which contracts are the most favourable for ensuring the environmental commitments of the Environmental Impact Statement are carried out. Early contractor involvement as well as construction contracts that incorporate maintenance, with monitoring, for an extended period afterwards were cited as key recommendations to ensure a good outcome for wildlife.
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