| 1. |
- Forsell, Håkan, 1968-
(författare)
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Den föränderliga staden : Staden. RJ årsbox 2020
- 2020
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- I det första häftet av RJ:s årsbox 2020 presenterar Håkan Forsell en ny epokindelning av den moderna stadens utveckling. Det är stadens föränderlighet som ligger till grund för analysen. Staden är både planerad och tillfällig.Enligt FN kommer närmare 70 procent av jordens befolkning att leva i städer år 2050. Antalet megastäder kommer att växa – men också mindre metropoler förväntas öka sin befolkning. Men staden innebär i sig en rad utmaningar som inte bara är ekologiska. Är det lämpligt att bo så tätt ihop? Vad innebär det? Stadens drar dessutom till sig våld. Så hur ska framtidens städer planeras och se ut? Och varför dras vi till städerna? Vilka behov fyller de?I RJ:s årsbox 2020 försöker ett antal forskare att svara på de frågorna och några till. Först ut är alltså stadshistorikern Håkan Forsell som gör en resa i den moderna stadens historia. För även om staden tycks stå pall, är den en plats i ständig rörelse och förändring.
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| 2. |
- Liu, Hong, et al.
(författare)
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On the maximum number of integer colourings with forbidden monochromatic sums
- 2021
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Ingår i: The Electronic Journal of Combinatorics. - : The Electronic Journal of Combinatorics. - 1097-1440 .- 1077-8926. ; 28:1
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Tidskriftsartikel (refereegranskat)abstract
- Let f(n, r) denote the maximum number of colourings of A ⊆ {1, …, n} with r colours such that each colour class is sum-free. Here, a sum is a subset {x, y, z} such that x + y = z. We show that f(n, 2) = 2⌈n/2⌉, and describe the extremal subsets. Further, using linear optimisation, we asymptotically determine the logarithm of f(n, r) for r ≤ 5. Similar results were obtained by Hán and Jiménez in the setting of finite abelian groups.
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| 3. |
- Liu, Hong, et al.
(författare)
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Stability from graph symmetrisation arguments with applications to inducibility
- 2023
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Ingår i: Journal of the London Mathematical Society. - : John Wiley & Sons. - 0024-6107 .- 1469-7750. ; 108:3, s. 1121-1162
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Tidskriftsartikel (refereegranskat)abstract
- We present a sufficient condition for the stability property of extremal graph problems that can be solved via Zykov's symmetrisation. Our criterion is stated in terms of an analytic limit version of the problem. We show that, for example, it applies to the inducibility problem for an arbitrary complete bipartite graph B, which asks for the maximum number of induced copies of B in an n-vertex graph, and to the inducibility problem for K2,1,1,1 and K3,1,1, the only complete partite graphs on at most five vertices for which the problem was previously open.
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| 4. |
- Morphis, Michaella, et al.
(författare)
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Evaluation of Iodine-123 and Iodine-131 SPECT activity quantification : a Monte Carlo study
- 2021
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Ingår i: EJNMMI Physics. - : Springer Science and Business Media LLC. - 2197-7364. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT studies, is influenced by the isotope-collimator combination as well as image corrections incorporated in the iterative reconstruction process. These factors can be investigated and optimised using Monte Carlo simulations. This study aimed to evaluate SPECT quantification accuracy for 123I with both the low-energy high resolution (LEHR) and medium-energy (ME) collimators and 131I with the high-energy (HE) collimator. Methods: Simulated SPECT projection images were reconstructed using the OS-EM iterative algorithm, which was optimised for the number of updates, with appropriate corrections for scatter, attenuation and collimator detector response (CDR), including septal scatter and penetration compensation. An appropriate calibration factor (CF) was determined from four different source geometries (activity-filled: water-filled cylindrical phantom, sphere in water-filled (cold) cylindrical phantom, sphere in air and point-like source), investigated with different volume of interest (VOI) diameters. Recovery curves were constructed from recovery coefficients to correct for partial volume effects (PVEs). The quantitative method was evaluated for spheres in voxel-based digital cylindrical and patient phantoms. Results: The optimal number of OS-EM updates was 60 for all isotope-collimator combinations. The CFpoint with a VOI diameter equal to the physical size plus a 3.0-cm margin was selected, for all isotope-collimator geometries. The spheres’ quantification errors in the voxel-based digital cylindrical and patient phantoms were less than 3.2% and 5.4%, respectively, for all isotope-collimator combinations. Conclusion: The study showed that quantification errors of less than 6.0% could be attained, for all isotope-collimator combinations, if corrections for; scatter, attenuation, CDR (including septal scatter and penetration) and PVEs are performed. 123I LEHR and 123I ME quantification accuracies compared well when appropriate corrections for septal scatter and penetration were applied. This can be useful in departments that perform 123I studies and may not have access to ME collimators.
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| 5. |
- Morphis, Michaella, et al.
(författare)
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Modelling of energy-dependent spectral resolution for SPECT Monte Carlo simulations using SIMIND
- 2021
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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo (MC) modelling techniques have been used extensively in Nuclear Medicine (NM). The theoretical energy resolution relationship (∝1/E−−√), does not accurately predict the gamma camera detector response across all energies. This study aimed to validate the accuracy of an energy resolution model for the SIMIND MC simulation code emulating the Siemens Symbia T16 dual-head gamma camera.MethodsMeasured intrinsic energy resolution data (full width half maximum (FWHM) values), for Ba-133, Lu-177, Am-241, Ga-67, Tc-99m, I-123, I-131 and F-18 sources in air, were used to create a fitted model of the energy response of the gamma camera. Both the fitted and theoretical models were used to simulate intrinsic and extrinsic energy spectra using three different scenarios (source in air; source in simple scatter phantom and a clinical voxel-based digital patient phantom).ResultsThe results showed the theoretical model underestimated the FWHM values at energies above 160.0 keV up to 23.5 keV. In contrast, the fitted model better predicted the measured FWHM values with differences less than 3.3 keV. The I-131 in-scatter energy spectrum simulated with the fitted model better matched the measured energy spectrum. Higher energy photopeaks, (I-123: 528.9 keV and I-131: 636.9 keV) simulated with the fitted model, more accurately resembled the measured photopeaks. The voxel-based digital patient phantom energy spectra, simulated with the fitted and theoretical models, showed the potential impact of an incorrect energy resolution model when simulating isotopes with multiple photopeaks.ConclusionModelling of energy resolution with the proposed fitted model enables the SIMIND user to accurately simulate NM images. A great improvement was seen for high-energy photon emitting isotopes (e.g. I-131), as well as isotopes with multiple photopeaks (e.g. Lu-177, I-131 and Ga-67) in comparison to the theoretical model. This will result in accurate evaluation of radioactivity quantification, which is vital for dosimetric purposes.
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| 6. |
- Morphis, Michaella, et al.
(författare)
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Validation of a SIMIND Monte Carlo modelled gamma camera for Iodine-123 and Iodine-131 imaging
- 2021
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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 7:6
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Monte Carlo (MC) modelling techniques can assess the quantitative accuracy of both planar and SPECT Nuclear Medicine images. It is essential to validate the MC code's capabilities in modelling a specific clinical gamma camera, for radionuclides of interest, before its use as a clinical image simulator. This study aimed to determine if the SIMIND MC code accurately simulates emission images measured with a Siemens Symbia™ T16 SPECT/CT system for I-123 with a LEHR and a ME collimator and for I-131 with a HE collimator. Methods: The static and WB planar validation tests included extrinsic system energy pulse-height distributions (EPHDs), system sensitivity and system spatial resolution in air as well as a scatter medium. The SPECT validation test comprised the sensitivity from a simple geometry of a sphere in a cylindrical water-filled phantom. Results: The system EPHDs compared well, with differences between measured and simulated primary photopeak FWHM values not exceeding 4.6 keV. Measured and simulated planar system sensitivity values displayed percentage differences less than 6.9% and 6.3% for static and WB planar images, respectively. Measured and simulated planar system spatial resolution values in air showed percentage differences not exceeding 6.4% (FWHM) and 10.0% (FWTM), and 5.1% (FWHM) and 5.4% (FWTM) for static and WB planar images, respectively. For static planar system spatial resolution measured and simulated in a scatter medium, percentage differences of FWHM and FWTM values were less than 5.8% and 12.6%, respectively. The maximum percentage difference between the measured and simulated SPECT validation results was 3.6%. Conclusion: The measured and simulated validation results compared well for all isotope-collimator combinations and showed that the SIMIND MC code could be used to accurately simulate static and WB planar and SPECT projection images of the Siemens Symbia™ T16 SPECT/CT for both I-123 and I-131 with their respective collimators.
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| 7. |
- Venter, Zander S., et al.
(författare)
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Green Apartheid : Urban green infrastructure remains unequally distributed across income and race geographies in South Africa
- 2020
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Ingår i: Landscape and Urban Planning. - : Elsevier BV. - 0169-2046 .- 1872-6062. ; 203
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Tidskriftsartikel (refereegranskat)abstract
- Urban green infrastructure provides ecosystem services that are essential to human wellbeing. A dearth of national-scale assessments in the Global South has precluded the ability to explore how political regimes, such as the forced racial segregation in South Africa during and after Apartheid, have influenced the extent of and access to green infrastructure over time. We investigate whether there are disparities in green infrastructure distributions across race and income geographies in urban South Africa. Using open-source satellite imagery and geographic information, along with national census statistics, we find that public and private green infrastructure is more abundant, accessible, greener and more treed in high-income relative to low-income areas, and in areas where previously advantaged racial groups (i.e. White citizens) reside. Areas with White residents report 6-fold higher income, have 11.7% greater tree cover, 8.9% higher vegetation greenness and live 700 m closer to a public park than areas with predominantly Black African, Indian, and Coloured residents. The inequity in neighborhood greenness levels has been maintained (for Indian and Coloured areas) and further entrenched (for Black African areas) since the end of Apartheid in 1994 across the country. We also find that these spatial inequities are mirrored in both private (gardens) and public (street verges, parks, green belts) spaces, hinting at the failure of governance structures to plan for and implement urban greening initiatives. By leveraging open-access satellite data and methods presented here, there is scope for civil society to monitor urban green infrastructure over time and thereby hold governments accountable to addressing environmental justice imperatives in the future.
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| 8. |
- Elfversson, Emma, 1983-, et al.
(författare)
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Den våldsamma staden
- 2020
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Bok (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Legeby, Ann, 1972-
(författare)
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Tillgänglighet i staden : Analyser ur ett systemperspektiv
- 2022
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Ingår i: Jämlik livsmiljö. - Stockholm : Kungliga tekniska högskolan. ; , s. 47-96
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Projektet Jämlik livsmiljö handlar om universell utformning och inom ramen för projektet vidareutvecklas modeller och metoder för stadsrumsanalys som specifikt handlar om utmaningar som rör funktionsnedsättningar. Arbetet är primärt inriktat på att fånga systemeffekter, hur hinder eller möjliggörande gestaltning påverkar tillgängligheten i staden i sig men också i relation till olika samhälleliga resurser.Delstudien Modell & metod har utforskat hur modellen av staden kan anpassas för att bättre spegla en viss typ av funktionsnedsättning eller en viss typ av behov. Målet är att klarlägga effekter av hinder respektive möjliggörare i den byggda miljön. I första hand gäller det effekter på systemet som helhet och inte primärt de helt lokala som annars är väl uppmärksammade inom universell design. Analyserna är framför allt inriktade på den byggda miljöns möjliggörande eller hindrande effekter för äldre och för personer med funktionsnedsättningar.För personer som behöver ”sitta för att kunna gå” så har sittplatser i stadens offentliga rum en avgörande betydelse. Analyser har genomförts vilka visar vilka stråk i Uppsala stad som är försedda med bänkar så att även de som behöver vila kan ta sig fram. Analyserna avslöjar även på ett mycket detaljerat sätt att det finns stora områden som kan beskrivas som ”bänköknar”, områden som präglas av en frånvaro av sittplatser. Det visar sig att detta inte bara får negativa konsekvenser för framkomligheten i sig, utan också för tillgängligheten till viktiga målpunkter, service och olika samhälleliga resurser.Resultatet ger värdefull kunskap om nuläget i staden och utgör ett träffsäkert planeringsunderlag. Det ger vägledning om vilka åtgärder som skulle behövas samt stöd för att formulera framtida strategier och policyer. Sammantaget bidrar tillvägagångssättet till att öka förståelsen för hur universell utformning kan integreras i processer som rör stadsbyggnad och gestaltingen av det offentliga rummet. I förlängningen kan detta stödja det långsiktiga målet om att bygga en stad tillgänglig för alla, oavsett ålder eller funktionsnedsättning.
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| 10. |
- Blennow, Anna, 1974
(författare)
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Den eviga staden
- 2020
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Bok (övrigt vetenskapligt/konstnärligt)
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