| 1. |
- Aamodt, K., et al.
(författare)
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The ALICE experiment at the CERN LHC
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3:S08002
-
Forskningsöversikt (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries, Its overall dimensions are 16 x 16 x 26 m(3) with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.
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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. |
- Hajkova, V., et al.
(författare)
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X-ray laser-induced ablation of lead compounds
- 2011
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Ingår i: DAMAGE TO VUV, EUV, AND X-RAY OPTICS III. - : SPIE.
-
Konferensbidrag (refereegranskat)abstract
- The recent commissioning of a X-ray free-electron laser triggered an extensive research in the area of X-ray ablation of high-Z, high-density materials. Such compounds should be used to shorten an effective attenuation length for obtaining clean ablation imprints required for the focused beam analysis. Compounds of lead (Z=82) represent the materials of first choice. In this contribution, single-shot ablation thresholds are reported for PbWO(4) and PbI(2) exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 J/cm(2) at 1.55 nm in lead tungstate although a value of 0.4 J/cm(2) is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm(2) at a FEL wavelength of 13.5 nm. Mechanisms of ablation processes are discussed to explain this discrepancy. Lead iodide shows at 1.55 nm significantly lower ablation threshold than tungstate although an attenuation length of the radiation is in both materials quite the same. Lower thermal and radiation stability of PbI(2) is responsible for this finding.
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| 4. |
- Hau-Riege, S. P., et al.
(författare)
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Wavelength dependence of the damage threshold of inorganic materials under extreme-ultraviolet free-electron-laser irradiation
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:11, s. 111104-111104-3
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Tidskriftsartikel (refereegranskat)abstract
- We exposed bulk SiC and films of SiC and B4C to single 25 fs long free-electron-laser pulses with wavelengths between 13.5 and 32 nm. The materials are candidates for x-ray free-electron laser optics. We found that the threshold for surface-damage of the bulk SiC samples exceeds the fluence required for thermal melting at all wavelengths. The damage threshold of the film sample shows a strong wavelength dependence. For wavelengths of 13.5 and 21.7 nm, the damage threshold is equal to or exceeds the melting threshold, whereas at 32 nm the damage threshold falls below the melting threshold.
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| 5. |
- Chalupsky, J., et al.
(författare)
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Characteristics of focused soft X-ray free-electron laser beam determined by ablation of organic molecular solids
- 2007
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Ingår i: Optics Express. - 1094-4087. ; 15:10, s. 6036-6043
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Tidskriftsartikel (refereegranskat)abstract
- A linear accelerator based source of coherent radiation, FLASH (Free-electron LASer in Hamburg) provides ultra-intense femtosecond radiation pulses at wavelengths from the extreme ultraviolet (XUV; lambda< 100nm) to the soft X-ray (SXR; lambda<30nm) spectral regions. 25-fs pulses of 32-nm FLASH radiation were used to determine the ablation parameters of PMMA - poly ( methyl methacrylate). Under these irradiation conditions the attenuation length and ablation threshold were found to be (56.9 +/- 7.5) nm and similar to 2 mJ center dot cm(-2), respectively. For a second wavelength of 21.7 nm, the PMMA ablation was utilized to image the transverse intensity distribution within the focused beam at mu m resolution by a method developed here.
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| 6. |
- Erkintalo, M., et al.
(författare)
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Numerical modelling of frequency comb generation in nonlinear resonators
- 2016
-
Ingår i: 16th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD 2016, Sydney, Australia, 11-15 July 2016. - 2158-3234. - 9781467386036 ; , s. 187-188
-
Konferensbidrag (refereegranskat)abstract
- We present a comprehensive review of recent work on numerical modelling of frequency comb generation in coherently-driven nonlinear resonators. Specifically, we discuss modelling and nonlinear dynamics of frequency combs generated in Kerr nonlinear microresonators, emphasizing links to similar dynamics studied in macroscopic fibre cavities. In addition to established Kerr frequency comb generators, we will also discuss emerging comb generation platforms based on continuously-driven quadratically nonlinear resonators.
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| 7. |
- Hau-Riege, S. P., et al.
(författare)
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Damage threshold of inorganic solids under free-electron-laser irradiation at 32.5 nm wavelength
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:17, s. 173128-
-
Tidskriftsartikel (refereegranskat)abstract
- Samples of B4C, amorphous C, chemical-vapor-deposition-diamond C, Si, and SiC were exposed to single 25 fs long pulses of 32.5 nm free-electron-laser radiation at fluences of up to 2.2 J/cm(2). The samples were chosen as candidate materials for x-ray free-electron-laser optics. It was found that the threshold for surface damage is on the order of the fluence required for thermal melting. For larger fluences, the crater depths correspond to temperatures on the order of the critical temperature, suggesting that the craters are formed by two-phase vaporization.
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| 8. |
- Boggio, J. M. Chavez, et al.
(författare)
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Efficient Kerr soliton comb generation in micro-resonator with interferometric back-coupling
- 2022
-
Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- Nonlinear Kerr micro-resonators have enabled fundamental breakthroughs in the understanding of dissipative solitons, as well as in their application to optical frequency comb generation. However, the conversion efficiency of the pump power into a soliton frequency comb typically remains below a few percent. We fabricate and characterize a hybrid Mach-Zehnder ring resonator geometry, consisting of a micro-ring resonator embedded in an additional cavity with twice the optical path length of the ring. The resulting interferometric back coupling enables to achieve an unprecedented control of the pump depletion: pump-to-frequency comb conversion efficiencies of up to 55% of the input pump power is experimentally demonstrated with a soliton crystal comb. We assess the robustness of the proposed on-chip geometry by generating a large variety of dissipative Kerr soliton combs, which require a lower amount of pump power to be accessed, when compared with an isolated micro-ring resonator with identical parameters. Micro-resonators with feedback enable accessing new regimes of coherent soliton comb generation, and are well suited for comb applications in astronomy, spectroscopy and telecommunications. Increasing the conversion efficiency of soliton crystals will enable further application of optical frequency comb. Here the authors engineer an hybrid Mach-Zehnder micro-ring resonator to achieve 80% pump-to-comb conversion efficiency based on dissipative Kerr solitons.
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| 9. |
- Boggio, J. M. Chavez, et al.
(författare)
-
Frequency comb generation in silicon nitride resonators with amplitude modulated pump
- 2021
-
Ingår i: LASER RESONATORS, MICRORESONATORS, AND BEAM CONTROL XXIII. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510641808
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Konferensbidrag (refereegranskat)abstract
- We investigate frequency comb generation in silicon nitride ring resonators by using a pump subject to a weak amplitude modulation. We show that a partial locking is obtained when the external modulation frequency differs from the resonator free-spectral-range by up to hundreds of MHz.
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| 10. |
- Chalupsky, J, et al.
(författare)
-
Non-thermal desorption/ablation of molecular solids induced by ultra-short soft x-ray pulses
- 2009
-
Ingår i: Optics Express. - 1094-4087. ; 17:1, s. 208-217
-
Tidskriftsartikel (refereegranskat)abstract
- We report the first observation of single-shot soft x-ray laser induced desorption occurring below the ablation threshold in a thin layer of poly ( methyl methacrylate) - PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg ( FLASH) at 21.7nm, the samples have been investigated by atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed and used to analyze single-shot imprints in PMMA. An intermediate regime of materials removal has been found, confirming model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm. Short-time exposure imprints provide sufficient information about transverse beam profile in HOH's tight focus whereas long-time exposed PMMA exhibits radiation-initiated surface hardening making the beam profile measurement infeasible. (C) 2008 Optical Society of America
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| 11. |
- Erkintalo, M., et al.
(författare)
-
Frequency combs in quadratically nonlinear resonators
- 2016
-
Ingår i: Optics InfoBase Conference Papers. - 2162-2701. - 9781943580170 ; , s. paper NM3A.1-
-
Konferensbidrag (refereegranskat)abstract
- We describe the physics and modelling of frequency combs and corresponding temporal patterns in coherently driven, quadratically nonlinear resonators.
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| 12. |
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| 13. |
- Leo, F., et al.
(författare)
-
Frequency-comb formation in doubly resonant second-harmonic generation
- 2016
-
Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 93:4
-
Tidskriftsartikel (refereegranskat)abstract
- We theoretically study the generation of optical frequency combs and corresponding pulse trains in doubly resonant intracavity second-harmonic generation (SHG). We find that, despite the large temporal walk-off characteristic of realistic cavity systems, the nonlinear dynamics can be accurately and efficiently modeled using a pair of coupled mean-field equations. Through rigorous stability analysis of the system's steady-state continuous-wave solutions, we demonstrate that walk-off can give rise to an unexplored regime of temporal modulation instability. Numerical simulations performed in this regime reveal rich dynamical behaviors, including the emergence of temporal patterns that correspond to coherent optical frequency combs. We also demonstrate that the two coupled equations that govern the doubly resonant cavity behavior can, under typical conditions, be reduced to a single mean-field equation akin to that describing the dynamics of singly-resonant-cavity SHG [F. Leo et al., Phys. Rev. Lett. 116, 033901 (2016)]. This reduced approach allows us to derive a simple expression for the modulation instability gain, thus permitting us to acquire significant insight into the underlying physics. We anticipate that our work will have a wide impact on the study of frequency combs in emerging doubly resonant cavity SHG platforms, including quadratically nonlinear microresonators.
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| 14. |
- Leo, F., et al.
(författare)
-
Theory of Frequency Comb Generation in Cavity Enhanced Second Harmonic Generation
- 2016
-
Ingår i: 2016 Conference on Lasers and Electro-Optics, CLEO 2016, San Jose, United States, 5-10 June 2016. - 2160-9020. - 9781943580118
-
Konferensbidrag (refereegranskat)abstract
- We theoretically investigate frequency comb generation in dispersive quadratically nonlinear resonators. We introduce a single mean field equation to model cavity enhanced second harmonic generation and find excellent agreement with recent experimental frequency comb observations.
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| 15. |
- Leo, F., et al.
(författare)
-
Walk-Off-Induced Modulation Instability, Temporal Pattern Formation, and Frequency Comb Generation in Cavity-Enhanced Second-Harmonic Generation
- 2016
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 116:3
-
Tidskriftsartikel (refereegranskat)abstract
- We derive a time-domain mean-field equation to model the full temporal and spectral dynamics of light in singly resonant cavity-enhanced second-harmonic generation systems. We show that the temporal walk-off between the fundamental and the second-harmonic fields plays a decisive role under realistic conditions, giving rise to rich, previously unidentified nonlinear behavior. Through linear stability analysis and numerical simulations, we discover a new kind of quadratic modulation instability which leads to the formation of optical frequency combs and associated time-domain dissipative structures. Our numerical simulations show excellent agreement with recent experimental observations of frequency combs in quadratic nonlinear media [Phys. Rev. A 91, 063839 (2015)]. Thus, in addition to unveiling a new, experimentally accessible regime of nonlinear dynamics, our work enables predictive modeling of frequency comb generation in cavity-enhanced second-harmonic generation systems. We expect our findings to have wide impact on the study of temporal and spectral dynamics in a diverse range of dispersive, quadratically nonlinear resonators.
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| 16. |
- Wabnitz, S., et al.
(författare)
-
Quadratic Optical Frequency Combs: Towards a New Platform for Multi-Octave Microcombs
- 2020
-
Ingår i: INTERNATIONAL CONFERENCE LASER OPTICS 2020 (ICLO 2020). - : IEEE. - 9781728152332
-
Konferensbidrag (refereegranskat)abstract
- Optical frequency comb sources based on three-wave-mixing in quadratic nonlinear materials allow for reduced pump power threshold and extended spectral coverage. We review recent progress on quadratic optical frequency combs based on second-harmonic generation and optical parametric oscillation.
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| 17. |
- Zitelli, M., et al.
(författare)
-
Spatiotemporal guided bullets in multimode fiber
- 2021
-
Ingår i: NONLINEAR FREQUENCY GENERATION AND CONVERSION: MATERIALS AND DEVICES XX. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510641761
-
Konferensbidrag (refereegranskat)abstract
- Beam self-imaging of ultrashort pulses in nonlinear graded-index (GRIN) multimode optical fibers is of interest for many applications, including spatiotemporal mode-locking in fiber lasers. We obtained a new analytical description for the nonlinear evolution of a laser beam of arbitrary transverse shape propagating in a GRIN fiber. The longitudinal beam evolution could be directly visualized by means of femtosecond laser pulses, propagating in the anomalous or in the normal dispersion regime, leading to light scattering out of the fiber core via the emission of blue photo-luminescence. As the critical power for self-focusing is approached and even surpassed, a host of previously undisclosed nonlinear effects is revealed, including strong multiphoton absorption by oxygen-deficiency center defects and Germanium inclusions, splitting and shifting of the self-imaging period, filamentation, and conical emission of the guided light bullets. We discovered that nonlinear loss has a profound influence on the process of high-order spatiotemporal soliton fission. The beam energy carried by the fiber is clamped to a fixed value, and nonlinear bullet attractors with suppressed Raman frequency shift and fixed temporal duration are generated, leading to highly efficient frequency conversion of the input near-infrared femtosecond pulses into mid-infrared multimode solitons.
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| 18. |
- Arabi, C. Mas, et al.
(författare)
-
Localized structures formed through domain wall locking in cavity-enhanced second-harmonic generation
- 2020
-
Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 45:20, s. 5856-5859
-
Tidskriftsartikel (refereegranskat)abstract
- We analyze the formation of localized structures in cavity-enhanced second-harmonic generation. We focus on the phase-matched limit, and consider that fundamental and generated waves have opposite signs of group velocity dispersion. We show that these states form due to the locking of domain walls connecting two stable homogeneous states of the system, and undergo collapsed snaking. We study the impact of temporal walk-off on the stability and dynamics of these localized states. (C) 2020 Optical Society of America
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| 19. |
- Blasiak, Robert, et al.
(författare)
-
The ocean genome and future prospects for conservation and equity
- 2020
-
Ingår i: Nature Sustainability. - : Springer Science and Business Media LLC. - 2398-9629. ; 3, s. 588-596
-
Forskningsöversikt (refereegranskat)abstract
- Life has evolved in the ocean for 3.7 billion years, resulting in a rich 'ocean genome', the ensemble of genetic material present in all marine biodiversity, including both the physical genes and the information they encode. Rapid advances in sequencing technologies and bioinformatics have enabled exploration of the ocean genome and are informing innovative approaches to conservation and a growing number of commercial biotechnology applications. However, the capacity to undertake genomic research and to access and use sequence data is inequitably distributed among countries, highlighting an urgent need to build capacity, promote inclusive innovation and increase access to affordable technologies. The ocean genome is the genetic material present in marine biodiversity. While technological advances are enabling exploration, conservation and innovation of this resource, the associated capacities are inequitably distributed among countries.
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| 20. |
- Crona, Beatrice, et al.
(författare)
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Four ways blue foods can help achieve food system ambitions across nations
- 2023
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 616:7955, s. 104-112
-
Tidskriftsartikel (refereegranskat)abstract
- Blue foods, sourced in aquatic environments, are important for the economies, livelihoods, nutritional security and cultures of people in many nations. They are often nutrient rich1, generate lower emissions and impacts on land and water than many terrestrial meats2, and contribute to the health3, wellbeing and livelihoods of many rural communities4. The Blue Food Assessment recently evaluated nutritional, environmental, economic and justice dimensions of blue foods globally. Here we integrate these findings and translate them into four policy objectives to help realize the contributions that blue foods can make to national food systems around the world: ensuring supplies of critical nutrients, providing healthy alternatives to terrestrial meat, reducing dietary environmental footprints and safeguarding blue food contributions to nutrition, just economies and livelihoods under a changing climate. To account for how context-specific environmental, socio-economic and cultural aspects affect this contribution, we assess the relevance of each policy objective for individual countries, and examine associated co-benefits and trade-offs at national and international scales. We find that in many African and South American nations, facilitating consumption of culturally relevant blue food, especially among nutritionally vulnerable population segments, could address vitamin B12 and omega-3 deficiencies. Meanwhile, in many global North nations, cardiovascular disease rates and large greenhouse gas footprints from ruminant meat intake could be lowered through moderate consumption of seafood with low environmental impact. The analytical framework we provide also identifies countries with high future risk, for whom climate adaptation of blue food systems will be particularly important. Overall the framework helps decision makers to assess the blue food policy objectives most relevant to their geographies, and to compare and contrast the benefits and trade-offs associated with pursuing these objectives.
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| 21. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Bichromatically pumped microresonator frequency combs
- 2014
-
Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 2469-9926 .- 2469-9934. ; 90:1
-
Tidskriftsartikel (refereegranskat)abstract
- A study is made of the nonlinear dynamics of bichromatically pumped microresonator Kerr frequency combs described by a driven and damped nonlinear Schrodinger equation, with an additional degree of freedom in the form of the modulation frequency. A truncated four-wave model is derived for the pump modes and the dominant sideband pair, which is found to be able to describe much of the essential dynamical behavior of the full equation. The stability of stationary states within the four-wave model is investigated, and numerical simulations are made to demonstrate that a large range of solutions, including cavity solitons, are possible beyond previously considered low-intensity patterns.
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| 22. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Complex temporal dynamics in optical cavities
- 2015
-
Ingår i: 2015 Spatiotemporal Complexity in Nonlinear Optics, SCNO 2015, Como, Italy, 31 August-4 September. - 9781467380614
-
Konferensbidrag (refereegranskat)abstract
- We overview recent advances in the modeling and understanding of complex spatiotemporal dynamics associated with the generation of optical frequency combs in microresonators.
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| 23. |
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| 24. |
- Hansson, Tobias, 1983, et al.
(författare)
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Dynamics of Frequency Comb Generation and Design of Planar Microring Resonators
- 2014
-
Ingår i: Proceedings of SIAM Conference on Nonlinear Waves and Coherent Structures, Cambridge UK, August 2014.
-
Konferensbidrag (refereegranskat)abstract
- We study the generation of optical frequency combs from microresonators and show that a truncated dynamical model can capture the essential nonlinear dynamics of both stable and chaotic patterns. We also present an analytical approach for obtaining linear and nonlinear design parameters of planar microring resonators. Closed form approximations for the eigenmode/eigenfrequency problem are derived for resonators possessing a large radius to width ratio and examples are presented for silicon microrings.
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| 25. |
- Hansson, Tobias, 1983, et al.
(författare)
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Dynamics of microresonator frequency comb generation: models and stability
- 2016
-
Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 5:2, s. 231-243
-
Forskningsöversikt (refereegranskat)abstract
- Microresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.
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| 26. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Frequency comb generation beyond the Lugiato-Lefever equation: multi-stability and super cavity solitons
- 2015
-
Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 32:7, s. 1259-1266
-
Tidskriftsartikel (refereegranskat)abstract
- The generation of optical frequency combs in microresonators is considered without resorting to the mean-field approximation. New dynamical regimes are found to appear for high intracavity power that cannot be modeled using the Lugiato-Lefever equation. Using the Ikeda map, we show the existence of multi-valued stationary states and analyze their stability. Period doubled patterns are considered, and a novel type of super cavity soliton associated with the multi-stable states is predicted.
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| 27. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Mid-infrared octave spanning frequency comb generation in silicon microrings
- 2014
-
Ingår i: European Conference on Optical Communication (ECOC) 2014. Cannes, France, September 2014.
-
Konferensbidrag (refereegranskat)abstract
- We numerically show that octave-spanning Kerr frequency comb generation in the MIR spectral region may be obtained from planar microring resonators, by combining analytical dispersion engineering with generalized nonlinear envelope equation simulations of the temporal frequency comb dynamics.
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| 28. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Mid-infrared soliton and Raman frequency comb generation in silicon microrings
- 2014
-
Ingår i: Optics Letters. - : The Optical Society. - 0146-9592 .- 1539-4794. ; 39:23, s. 6747-6750
-
Tidskriftsartikel (refereegranskat)abstract
- We numerically study the mechanisms of frequency comb generation in the mid-infrared spectral region from cw-pumped silicon microring resonators. Coherent soliton comb generation may be obtained even for a pump with zero linear cavity detuning, through suitable control of the effective lifetime of free carriers from multiphoton absorption, which introduces a nonlinear cavity detuning via free-carrier dispersion. Conditions for optimal octave spanning Raman comb generation are also described.
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| 29. |
- Hansson, Tobias, 1983, et al.
(författare)
-
Multi-stability and super cavity solitons in microresonator frequency combs
- 2015
-
Ingår i: Integrated Photonics Research, Silicon and Nanophotonics, IPRSN 2015, Boston, United States; 27 June - 1 July 2015. - 9781557520005
-
Konferensbidrag (refereegranskat)abstract
- Frequency comb generation in microresonators is considered beyond the meanfield approximation. We show the appearance of multi-valued stationary states and predict the existence of a novel type of super cavity solitons.
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| 30. |
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| 31. |
- Hansson, Tobias, et al.
(författare)
-
Quadratic cavity soliton optical frequency combs
- 2019
-
Ingår i: 2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO). - : IEEE. - 9781943580576
-
Konferensbidrag (refereegranskat)abstract
- We theoretically investigate the formation of frequency combs in a dispersive second-harmonic generation cavity system, and predict the existence of quadratic cavity solitons in the absence of a temporal walk-off. (C) 2019 The Author(s)
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| 32. |
- Johnsson, Per, et al.
(författare)
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Attosecond electron wave packet dynamics in strong laser fields
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:1, s. 1-013001
-
Tidskriftsartikel (refereegranskat)abstract
- We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (similar to 20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes.
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| 33. |
- Mangini, F., et al.
(författare)
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Self-imaging dynamics in nonlinear GRIN multimode optical fibers
- 2020
-
Ingår i: Optics InfoBase Conference Papers. - : Optica Publishing Group. - 9781943580804
-
Konferensbidrag (refereegranskat)abstract
- We study nonlinear self-imaging dynamics in graded-index multimode optical fibers. Side-scattering of light that accompanies the propagation of intense femtosecond pulses permits us to directly measure the self-imaging period.
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| 34. |
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| 35. |
- Parra-Rivas, P., et al.
(författare)
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Locking of Domain Walls and Quadratic Frequency Combs in Doubly Resonant Optical Parametric Oscillators
- 2019
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Konferensbidrag (refereegranskat)abstract
- The formation of frequency combs (FCs) in high-Q microresonators with Kerr type of nonlinearity has attracted a lot of attention in the past decade [1]. Recently it has been shown that FCs can be also generated in dissipative dispersive cavities with quadratic nonlinearities [2,3], opening a new possibility of generating combs in previously unattainable spectral regions. Previous work has shown that modulational instability (MI) induces pattern and FC formation in degenerate optical parametric oscillators (OPOs) [4]. However, the existence of dissipative solitons or localized structures (LSs) is still unclear. In this work we present the locking of domain walls (DWs) as an alternative mechanism to MI for the formation of LSs and FCs. DWs have been widely studied in the context of Kerr cavities and diffractive OPO cavities [5,6]. Here we show that similar structures can arise in dispersive quadratic cavities. To illustrate this, we consider a dispersive cavity with a quadratic medium phase matched for degenerate OPO and driven by the field B in at the frequency 2ω 0 in a doubly resonant configuration. The formation of dissipative structures in this type of cavity can be described by an infinite map for the slowly varying electric field envelopes A m , and B m , that are centered at frequency ω 0 and 2ω 0 , respectively [4], where m indicates the cavity round-trip number. With this map one may numerically explore the dynamics of the system. For example, Fig. 1(a)-(b) show the formation of a dissipative structure, after a sufficient number of round-trips (m = 2 · 10 4 ), from an initial noisy background. We see that i) both fields are phase locked and drift at the same velocity; ii) for the A field one can identify a sequence of DWs connecting two different, and coexisting, CW states, that form a disordered structure. Furthermore, the latter is composed of a sequence of LSs of different widths. One of them, LS 4 , is plotted in panel (c). We demonstrate that this ty...
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| 36. |
- Pereira, Laura M., et al.
(författare)
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The living infinite: Envisioning futures for transformed human-nature relationships on the high seas
- 2023
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Ingår i: Marine Policy. - 0308-597X .- 1872-9460. ; 153, s. 105644-105644
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Tidskriftsartikel (refereegranskat)abstract
- We find ourselves at a critical crossroads for the future governance of the high seas, but the perceived remoteness of the global ocean creates a psychological barrier for people to engage with it. Given challenges of overexploitation, inequitable access and other sustainability and equity concerns, current ocean governance mechanisms are not fit-for-purpose. This decade offers opportunities for direct impact on ocean governance, however, triggering a global transformation on how we use and protect the half of our planet requires a concerted effort that is guided by shared values and principles across regions and sectors. The aim of the series of workshops outlined in this paper, was to undertake a futures thinking process that could use the Nature Futures Framework as a mechanism to bring more transformative energy into how humans conceptualise the high seas and therefore how we aim to govern the ocean. We found that engaging with the future through science fiction narratives allowed a more radical appreciation of what could be and infusing science with artistic elements can inspire audiences beyond academia. Thus, creative endeavours of co-production that promote and encourage imagination to address current challenges should be considered as important tools in the science-policy interface, also as a way to elicit empathetic responses. This workshop series was a first, and hopefully promising, step towards generating a more creative praxis in how we imagine and then act for a better future for the high seas.
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| 37. |
- Pifferi, A, et al.
(författare)
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Performance assessment of photon migration instruments: the MEDPHOT protocol
- 2005
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Ingår i: Applied Optics. - 2155-3165. ; 44:11, s. 2104-2114
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Tidskriftsartikel (refereegranskat)abstract
- We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.
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| 38. |
- Short, Rebecca E., et al.
(författare)
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Harnessing the diversity of small-scale actors is key to the future of aquatic food systems
- 2021
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Ingår i: Nature Food. - : Springer Science and Business Media LLC. - 2662-1355. ; 2:9, s. 733-741
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Tidskriftsartikel (refereegranskat)abstract
- Small-scale fisheries and aquaculture (SSFA) provide livelihoods for over 100 million people and sustenance for -1 billion people, particularly in the Global South. Aquatic foods are distributed through diverse supply chains, with the potential to be highly adaptable to stresses and shocks, but face a growing range of threats and adaptive challenges. Contemporary governance assumes homogeneity in SSFA despite the diverse nature of this sector. Here we use SSFA actor profiles to capture the key dimensions and dynamism of SSFA diversity, reviewing contemporary threats and exploring opportunities for the SSFA sector. The heuristic framework can inform adaptive governance actions supporting the diversity and vital roles of SSFA in food systems, and in the health and livelihoods of nutritionally vulnerable people-supporting their viability through appropriate policies whilst fostering equitable and sustainable food systems.
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| 39. |
- Spijkers, Jessica, et al.
(författare)
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Exploring the future of fishery conflict through narrative scenarios
- 2021
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Ingår i: One Earth. - : Elsevier BV. - 2590-3330 .- 2590-3322. ; 4:3, s. 386-396
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies suggest that the pervasive impacts on global fishery resources caused by stressors such as overfishing and climate change could dramatically increase the likelihood of fishery conflict. However, existing projections do not consider wider economic, social, or political trends when assessing the likelihood of, and influences on, future conflict trajectories. In this paper, we build four future fishery conflict scenarios by considering multiple fishery conflict drivers derived from an expert workshop, a longitudinal database of international fishery conflict, secondary data on conflict driver trends, and regional expert reviews. The scenarios take place between the years 2030 and 2060 in the North-East Atlantic (scramble for the Atlantic''), the East China Sea (the remodeled empire''), the coast of West Africa (oceanic decolonization''), and the Arctic (polar renaissance''). The scenarios explore the implications of ongoing trends in conflict-prone regions of the world and function as accessible, science-based communication tools that can help foster anticipatory governance capacity in the pursuit of future ocean security.
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| 40. |
- Spijkers, Jessica, et al.
(författare)
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Identifying predictors of international fisheries conflict
- 2021
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Ingår i: Fish and Fisheries. - : Wiley. - 1467-2960 .- 1467-2979. ; 22:4, s. 834-850
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Tidskriftsartikel (refereegranskat)abstract
- Marine capture fishery resources are declining, and demand for them is rising. These trends are suspected to incite conflict, but their effects have not been quantitatively examined. We applied a multi-model ensemble approach to a global database of international fishery conflicts between 1974 and 2016 to test the supply-induced scarcity hypothesis (diminishing supplies of fishery resources increase fisheries conflict), the demand-induced scarcity hypothesis (rising demand for fishery resources increases fisheries conflict), and three alternative political and economic hypotheses. While no single indicator was able to fully explain international conflict over fishery resources, we found a positive relationship between increased conflict over fishery resources and higher levels of per capita GDP for the period 1975-1996. For the period 1997-2016, we found evidence supporting the demand-induced scarcity hypothesis, and the notion that an increase in supply of fishery resources is linked to an increase in conflict occurrence. By identifying significant predictors of international fisheries conflict, our analysis provides useful information for policy approaches for conflict anticipation and management.
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| 41. |
- Spinelli, L., et al.
(författare)
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Determination of reference values for optical properties of liquid phantoms based on Intralipid and India ink
- 2014
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Ingår i: Biomedical Optics Express. - : Optical Society of America. - 2156-7085. ; 5:7, s. 2037-2053
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Tidskriftsartikel (refereegranskat)abstract
- A multi-center study has been set up to accurately characterize the optical properties of diffusive liquid phantoms based on Intralipid and India ink at near-infrared (NIR) wavelengths. Nine research laboratories from six countries adopting different measurement techniques, instrumental set-ups, and data analysis methods determined at their best the optical properties and relative uncertainties of diffusive dilutions prepared with common samples of the two compounds. By exploiting a suitable statistical model, comprehensive reference values at three NIR wavelengths for the intrinsic absorption coefficient of India ink and the intrinsic reduced scattering coefficient of Intralipid-20% were determined with an uncertainty of about 2% or better, depending on the wavelength considered, and 1%, respectively. Even if in this study we focused on particular batches of India ink and Intralipid, the reference values determined here represent a solid and useful starting point for preparing diffusive liquid phantoms with accurately defined optical properties. Furthermore, due to the ready availability, low cost, long-term stability and batch-to-batch reproducibility of these compounds, they provide a unique fundamental tool for the calibration and performance assessment of diffuse optical spectroscopy instrumentation intended to be used in laboratory or clinical environment. Finally, the collaborative work presented here demonstrates that the accuracy level attained in this work for optical properties of diffusive phantoms is reliable.
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| 42. |
- Tigchelaar, Michelle, et al.
(författare)
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Compound climate risks threaten aquatic food system benefits
- 2021
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Ingår i: Nature Food. - : Springer Science and Business Media LLC. - 2662-1355. ; 2:9, s. 673-682
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Tidskriftsartikel (refereegranskat)abstract
- The nutritional, economic and livelihood contributions provided by aquatic food systems are threatened by climate change. Building climate resilience requires systemic interventions that reduce social vulnerabilities. Aquatic foods from marine and freshwater systems are critical to the nutrition, health, livelihoods, economies and cultures of billions of people worldwide, but climate-related hazards may compromise their ability to provide these benefits. Here, we estimate national-level aquatic food system climate risk using an integrative food systems approach that connects climate hazards impacting marine and freshwater capture fisheries and aquaculture to their contributions to sustainable food system outcomes. We show that without mitigation, climate hazards pose high risks to nutritional, social, economic and environmental outcomes worldwide-especially for wild-capture fisheries in Africa, South and Southeast Asia, and Small Island Developing States. For countries projected to experience compound climate risks, reducing societal vulnerabilities can lower climate risk by margins similar to meeting Paris Agreement mitigation targets. System-level interventions addressing dimensions such as governance, gender equity and poverty are needed to enhance aquatic and terrestrial food system resilience and provide investments with large co-benefits towards meeting the Sustainable Development Goals.
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| 43. |
- Tigchelaar, Michelle, et al.
(författare)
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The vital roles of blue foods in the global food system
- 2022
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Ingår i: Global Food Security. - : Elsevier BV. - 2211-9124. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- Blue foods play a central role in food and nutrition security for billions of people and are a cornerstone of the livelihoods, economies, and cultures of many coastal and riparian communities. Blue foods are extraordinarily diverse, are often rich in essential micronutrients and fatty acids, and can often be produced in ways that are more environmentally sustainable than terrestrial animal-source foods. Capture fisheries constitute the largest wild-food resource for human extraction that would be challenging to replace. Yet, despite their unique value, blue foods have often been left out of food system analyses, policies, and investments. Here, we focus on three imperatives for realizing the potential of blue foods: (1) Bring blue foods into the heart of food system decision-making; (2) Protect and develop the potential of blue foods to help end malnutrition; and (3) Support the central role of small-scale actors in fisheries and aquaculture. Recognition of the importance of blue foods for food and nutrition security constitutes a critical justification to preserve the integrity and diversity of aquatic species and ecosystems.
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| 44. |
- Wabnitz, K, et al.
(författare)
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National Planetary Health learning objectives for Germany: A steppingstone for medical education to promote transformative change
- 2023
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Ingår i: Frontiers in public health. - : Frontiers Media SA. - 2296-2565. ; 10, s. 1093720-
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Tidskriftsartikel (refereegranskat)abstract
- Physicians play an important role in adapting to and mitigating the adverse health effects of the unfolding climate and ecological crises. To fully harness this potential, future physicians need to acquire knowledge, values, skills, and leadership attributes to care for patients presenting with environmental change-related conditions and to initiate and propel transformative change in healthcare and other sectors of society including, but not limited to, the decarbonization of healthcare systems, the transition to renewable energies and the transformation of transport and food systems. Despite the potential of Planetary Health Education (PHE) to support medical students in becoming agents of change, best-practice examples of mainstreaming PHE in medical curricula remain scarce both in Germany and internationally. The process of revising and updating the Medical Licensing Regulations and the National Competency-based Catalog of Learning Objectives for Medical Education in Germany provided a window of opportunity to address this implementation challenge. In this article, we describe the development and content of national Planetary Health learning objectives for Germany. We anticipate that the learning objectives will stimulate the development and implementation of innovative Planetary Health teaching, learning and exam formats in medical schools and inform similar initiatives in other health professions. The availability of Planetary Health learning objectives in other countries will provide opportunities for cross-country and interdisciplinary exchange of experiences and validation of content, thus supporting the consolidation of Planetary Health learning objectives and the improvement of PHE for all health professionals globally.
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