Fast algorithms and efficient GPU implementations for the Radon transform and the back-projection operator represented as convolution operators

The Radon transform and its adjoint, the back-projection operator, can both be expressed as convolutions in log-polar coordinates. Hence, fast algorithms for the application of the operators can be constructed by using FFT, if data is resampled at log-polar coordinates. Radon data is typically measured on an equally spaced grid in polar coordinates, and reconstructions are represented (as images) in Cartesian coordinates. Therefore, in addition to FFT, several steps of interpolation have to be conducted in order to apply the Radon transform and the back-projection operator by means of convolutions. Both the interpolation and the FFT operations can be efficiently implemented on Graphical Processor Units (GPUs). For the interpolation, it is possible to make use of the fact that linear interpolation is hard-wired on GPUs, meaning that it has the same computational cost as direct memory access. Cubic order interpolation schemes can be constructed by combining linear interpolation steps which provides important computation speedup. We provide details about how the Radon transform and the back-projection can be implemented efficiently as convolution operators on GPUs. For large data sizes, speedups of about 10 times are obtained in relation to the computational times of other software packages based on GPU implementations of the Radon transform and the back-projection operator. Moreover, speedups of more than a 1000 times are obtained against the CPU-implementations provided in the MATLAB image processing toolbox

Ecological Modernization and the European Greens

Green political parties are traditionally known to strive for radical systematic change in favor of the environment. The radical demands might limit the voter support and consequently the possibility of coalition collaborations. However, Green parties have permanently established themselves in various parliaments throughout Europe. This thesis argues that an ideological transformation has occurred, which enables Green parties to increase parliamentary policy influence. Moreover, the study has a mixed methods approach. The quantitative research is conducted on all well established European Green parties, followed by qualitative case studies on three specific Green parties. The hypothesis implies that the internal ideological transformation can be explained as a shift from traditional Ecologism towards Ecological Modernization. By conducting ideal type analysis on the cases selected, the study finds support for the hypothesis, and an ideological transformation can be confirmed. The results are discussed and a potential reason for the transformation is found to be the strive for increased policy influence. However, further research is needed in order to confirm this hypothesis.Miljöpartier har växt fram på den Europeiska politiska arenan. På ett par decennium har Miljöpartier förändrats från en radikal miljörörelse till att vara ett konkret regeringsalternativ. Denna strävan efter policyinflytande går emot de traditionella gröna ideologin. Studiens syfte är att förstå om en ideologisk förändring har ägt rum bland Europas Miljöpartier, samt vad detta kan bero på. Den traditionella gröna ideologin, eller traditionell Ekologism som jag benämner den i studien, strävar efter radikal förändring av miljöpolicy. Genom att reformera det ekonomiska systemet kraftigt samt genom att förändra och begränsa den nuvarande levnadsstandarden, kan mänskligheten leva i harmoni med naturen. Dessa radikala krav på förändring skiljer sig kraftigt från andra mer traditionella politiska partier och konsekvensen blev ett begränsat väljarstöd för de olika Miljöpartierna. Den generella väljaren var inte beredd att reducera sin levnadsstandard till förmån för miljön. Detta medförde att Miljöpartierna inte valde att sträva mot ett ökat direkt policyinflytande inom de nationella parlamenten, utan strävade snarare efter att påverka de andra partierna i parlamenten från opposition, genom att ständigt påminna om vikten av miljöpolicy. Trots detta så har Miljöpartier på senare år ingått i koalitioner vilket i vissa fall till och med har medfört regeringsproposition. En tydlig ideologisk förändring har uppfattats, och min hypotes indikerar att förändringen kan förklaras med hjälp av teorin Ekologisk Modernisering. Ekologisk Modernisering möjliggör en annan typ av miljöpolicy, utan att ställa radikala krav på begränsad levnadsstandard. Genom att kombinera ekonomiska och gröna värden kan ekonomisk tillväxt uppnås på ett hållbart sätt. Teknologiska innovationer ses som en viktig del i lösningen på miljöproblemen och teknologitilliten är stor inom teorin. Förespråkare av teorin menar även att en grön ekonomi kommer gynna forskning och framtagande av ny miljövänlig teknik. Enligt förespråkare för Ekologisk Modernisering krävs alltså ingen radikal förändring inom det ekonomiska systemet eller inom levnadsstandard för att agera till förmån för miljön. Studien är genomförd i två steg. Först genom en statistisk undersökning på alla Europeiska Miljöpartier som har blivit invalda i sina respektive nationella parlament, i minst fyra val i sträck. Sedan har fallstudier genomförts på tre av fallen från den statiska undersökningen (Sverige, Irland och Tyskland), med målsättningen att få en mer djupgående förståelse för den ideologiska förändringen. Fallstudierna bekräftar att en ideologisk förändring har skett i linje med hypotesen, men då urvalet inte är slumpmässigt så kan studien enbart bevisa en förändring inom de fall som faktiskt undersöks. Det statistiska resultatet indikerar att fallstudieresultatet möjligen kan gälla ur ett mer generellt Europeiskt perspektiv, men vidare forskning krävs för att bekräfta detta. En potentiell anledning till den ideologiska förändringen är strävan efter ökat policyinflytande. Då Ekologisk Modernisering möjliggör miljöpolicy utan krav på radikal förändring, kan väljarstödet öka. Ett ökat väljarstöd kan i sin tur möjliggöra att Miljöpartier kan tackla miljöproblemen från en högre policyinstans. Alla tre fall som studerats i uppsatsen har gått från att aktivt inte sträva efter regeringsmedverkan, till att ingå i koalitioner med målsättningen att nå regering. Kompromissen som ett koalitionssamarbete medför, begränsar möjligheterna till miljöpolicy-skapande. Vidare forskning krävs för att förstå i vilken mån lägre krav på förändring, i kombination med ett ökat direkt policyinflytande, medför bättre eller sämre påverkan på miljön jämfört med de traditionella Miljöpartierna

Non-Convex Rank/Sparsity Regularization and Local Minima

This paper considers the problem of recovering either a low rank matrix or a sparse vector from observations of linear combinations of the vector or matrix elements. Recent methods replace the non-convex regularization with $\ell_1$ or nuclear norm relaxations. It is well known that this approach can be guaranteed to recover a near optimal solutions if a so called restricted isometry property (RIP) holds. On the other hand it is also known to perform soft thresholding which results in a shrinking bias which can degrade the solution. In this paper we study an alternative non-convex regularization term. This formulation does not penalize elements that are larger than a certain threshold making it much less prone to small solutions. Our main theoretical results show that if a RIP holds then the stationary points are often well separated, in the sense that their differences must be of high cardinality/rank. Thus, with a suitable initial solution the approach is unlikely to fall into a bad local minima. Our numerical tests show that the approach is likely to converge to a better solution than standard $\ell_1$/nuclear-norm relaxation even when starting from trivial initializations. In many cases our results can also be used to verify global optimality of our method

Four-dimensional tomographic reconstruction by time domain decomposition

Since the beginnings of tomography, the requirement that the sample does not change during the acquisition of one tomographic rotation is unchanged. We derived and successfully implemented a tomographic reconstruction method which relaxes this decades-old requirement of static samples. In the presented method, dynamic tomographic data sets are decomposed in the temporal domain using basis functions and deploying an L1 regularization technique where the penalty factor is taken for spatial and temporal derivatives. We implemented the iterative algorithm for solving the regularization problem on modern GPU systems to demonstrate its practical use

Fast hyperbolic Radon transform represented as convolutions in log-polar coordinates

The hyperbolic Radon transform is a commonly used tool in seismic processing, for instance in seismic velocity analysis, data interpolation and for multiple removal. A direct implementation by summation of traces with different moveouts is computationally expensive for large data sets. In this paper we present a new method for fast computation of the hyperbolic Radon transforms. It is based on using a log-polar sampling with which the main computational parts reduce to computing convolutions. This allows for fast implementations by means of FFT. In addition to the FFT operations, interpolation procedures are required for switching between coordinates in the time-offset; Radon; and log-polar domains. Graphical Processor Units (GPUs) are suitable to use as a computational platform for this purpose, due to the hardware supported interpolation routines as well as optimized routines for FFT. Performance tests show large speed-ups of the proposed algorithm. Hence, it is suitable to use in iterative methods, and we provide examples for data interpolation and multiple removal using this approach.Comment: 21 pages, 10 figures, 2 table

Integration of algae-based biofuel production with an oil refinery: Energy and carbon footprint assessment

Biofuel production from algae feedstock has become a topic of interest in the recent decades since algae biomass cultivation is feasible in aquaculture and does therefore not compete with use of arable land. In the present work, hydrothermal liquefaction of both microalgae and macroalgae is evaluated for biofuel production and compared with transesterifying lipids extracted from microalgae as a benchmark process. The focus of the evaluation is on both the energy and carbon footprint performance of the processes. In addition, integration of the processes with an oil refinery has been assessed with regard to heat and material integration. It is shown that there are several potential benefits of co-locating an algae-based biorefinery at an oil refinery site and that the use of macroalgae as feedstock is more beneficial than the use of microalgae from a system energy performance perspective. Macroalgae-based hydrothermal liquefaction achieves the highest system energy efficiency of 38.6%, but has the lowest yield of liquid fuel (22.5 MJ per 100 MJalgae) with a substantial amount of solid biochar produced (28.0 MJ per 100 MJalgae). Microalgae-based hydrothermal liquefaction achieves the highest liquid biofuel yield (54.1 MJ per 100 MJalgae), achieving a system efficiency of 30.6%. Macro-algae-based hydrothermal liquefaction achieves the highest CO2 reduction potential, leading to savings of 24.5 resp 92 kt CO2eq/year for the two future energy market scenarios considered, assuming a constant feedstock supply rate of 100 MW algae, generating 184.5, 177.1 and 229.6 GWhbiochar/year, respectively. Heat integration with the oil refinery is only possible to a limited extent for the hydrothermal liquefaction process routes, whereas the lipid extraction process can benefit to a larger extent from heat integration due to the lower temperature level of the process heat demand

Experimental Investigation of the Effect of Random Packings on Heat Transfer and Particle Segregation in Packed-Fluidized Bed

The heat transfer coefficient, pressure drop, and vertical segregation in a\ua0bubbling fluidized bed reactor containing random packings were investigated. The bed\ua0material was silica sand in the size range of 90−400 μm. Experiments were done for bed\ua0temperatures ranging from 400 to 900 \ub0C and superficial gas velocities up to 0.411 m/s.\ua0Five different types of packings were evaluated: (i) RMSR (25 mm stainless steel thread\ua0saddle ring), (ii) Hiflow (25 mm stainless steel pall ring), (iii) RR6 (6 mm ceramic\ua0Raschig ring), (iv) RR10 (10 mm ceramic Raschig ring), and (v) ASB (12.7 mmaluminum silicate balls). The RMSR packing showed an increase in the heat transfer\ua0coefficient (up to 1243 W/m2\ua0K), as compared to bubbling beds with no packings (up\ua0to 1124 W/m2\ua0K). Also, beds with RMSR and Hiflow packings had a lower pressure\ua0drop and vertical segregation compared to low void factor packings such as RR6, RR10,\ua0and ASB

Socionom - Hjälpare på heltid, deltid eller övertid?

Abstract Author: Viktor Andersson & Daniel Pettersson Title: Social worker – Helper on full-time, part-time or overtime? A qualitative study about the perception of work and leisure in social work. Supervisor: Johan Cronehed There is a lively discussion in the community about what work is and what leisure is. The aim of our study was to look at how professional social workers set up to be social workers with a helping function beyond their working hours, at their leisure. Our study was conducted through interviews with social workers who are employed on full time in social services, residential treatment and school counselors. The method used to generate our empirical materials were inductive which means that the theory was selected by the empirical material. To analyze the collected empirical material, we used a theoretical basis approach that was rational choice. A general conclusion of our study was that social workers are keen to draw boundaries for what is work and what is leisure. This distinction is mainly an expressed desire, and what we have seen is that it is hard to maintain the desire in reality. There are however, according to the study, a conclusion that there is a pain threshold for where the line is to help in their spare time. The study also shows how social workers as professionals feels about giving money to beggars in their spare time outside their profession. The study shows that social worker means that there is a consensus that the knowledge by the profession is why the professional social workers is not donating money to beggars on either leisure or work time, because they do not think it helps. There is also a pattern in our empirical work that shows that social work is a little more than just a profession despite the fact that social workers being involved in the study says that social work is more of a career choice than a life missio