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- Hernandez-Andrade, Edgar, et al.
(author)
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Lung fractional moving blood volume in normally grown and growth restricted foetuses.
- 2004
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In: Clinical Physiology and Functional Imaging. - 1475-0961. ; 24:2, s. 69-74
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Journal article (peer-reviewed)abstract
- Objective: To examine foetal lung blood perfusion using power Doppler ultrasound (PDU) and to compare fractional moving blood volume (FMBV) and mean pixel intensity (MPI) estimations in the lungs of normally grown (NG) foetuses and foetuses with intrauterine growth restriction (IUGR) and also to correlate foetal lung FMBV and MPI with respiratory complications after birth. Methods: Lungs of 47 NG and 25 IUGR foetuses after 32 weeks of gestation were examined with PDU. FMBV and MPI were estimated in a defined region in the posterior part of the foetal lung closest to maternal abdominal wall. FMBV and MPI were correlated to foetal weight deviation and gestational age. Perinatal outcome and respiratory complications after birth were recorded in both groups. Results: There were significantly lower FMBV and MPI values in IUGR than in NG foetuses. The overall variation was lower for FMBV than for MPI. There was a slightly higher correlation between FMBV and foetal weight deviation [r = 0·33, 95% confidence intervals (CI) 0·11-0·52] than between MPI and foetal weight deviation (r = 0·26, 95% CI 0·03-0·46). There was no significant correlation between FMBV or MPI and gestational age. No differences between the groups were found in the rate of respiratory complications, and they were not correlated either to the FMBV or MPI. Conclusion: FMBV and MPI, estimated from the PDU signals of foetal lung circulation, showed lower values in third-trimester pregnancies complicated by IUGR. The frequency of neonatal respiratory complications was not increased in cases with low pulmonary FMBV and MPI values.
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- Jansson, Tomas, et al.
(author)
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Frequency dependence of speckle in continuous-wave ultrasound with implications for blood perfusion measurements.
- 2002
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In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010. ; 49:6, s. 715-725
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Journal article (peer-reviewed)abstract
- Speckle in continuous wave (CW) Doppler has previously been found to cause large variations in detected Doppler power in blood perfusion measurements, where a large number of blood vessels are present in the sample volume. This artifact can be suppressed by using a number of simultaneously transmitted frequencies and averaging the detected signals. To optimize the strategy, statistical properties of speckle in CW ultrasound need to be known. This paper presents analysis of the frequency separation necessary to obtain independent values of the received power for CW ultrasound using a simplified mathematical model for insonation of a static, lossless, statistically homogeneous, weakly scattering medium. Specifically, the autocovariance function for received power is derived, which functionally is the square of the (deterministic) autocorrelation function of the effective sample volumes produced by the transducer pair for varying frequencies, at least if a delta correlated medium is assumed. A marginal broadening of the modeled autocovariance functions is expected for insonation of blood. The theory is applicable to any transducer aperture, but has been experimentally verified here with 5-MHz, 6.35-mm circular transducers using an agar phantom containing small, randomly dispersed glass particles. A similar experimental verification of a transducer used in multiple-frequency blood perfusion measurements shows that the model proposed in this paper is plausible for explaining the decorrelation between different channels in such a measurement.
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- Jansson, Tomas, et al.
(author)
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Introduktion till projektledning : ABC i projektledningsmetodik och organisationens projektmiljö
- 2003
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Book (peer-reviewed)abstract
- Den här boken är en lärobok, en introduktion till projektledning. Bokens fokus ligger inom området Projektledningsmetodik. Övriga direkt projektledningsrelaterade områden Projektledarskap och Organisationens projektmiljö berörs kortfattat för att ge den referensram som behövs för att kunna ta del av bokens huvudbudskap. Boken är indelad i fyra huvudavsnitt:I avsnittet Projektledningsbegrepp diskuterar vi begrepp som är grundläggande i projektsammanhang, som t ex projekt, projektarbetsform och projektledare. Vi diskuterar också i vilka sammanhang och i vilka typer av projekt det är meningsfullt att tala om yrkesmässig projektledning.I Organisationens projektmiljö diskuterar vi projektens roll i förhållande till verksamhetsprocesser och till linjeorganisationen i den verksamhet där projektet genomförs. Vi går också igenom de aspekter som projektmodeller vanligen omfattar: roller, faser, affärsbeslut och ledningsdokument i projekt.Avsnittet Projektledarskap diskuterar vilka situationer projektledare typiskt ställs inför när de leder människor i projekt. Avsnittet Projektledningsmetodik är bokens huvuddel. Där beskriver vi grundläggande tekniker som används för att definiera, avgränsa, planera, organisera, leda, överlämna och avsluta ett projekt. Dessa tekniker är projektledarens verktygslåda.Vi delar upp avsnittet i dels hur man arbetar fram en bra projektplan och dels hur man använder planerna under projektgenomförandet. Vi visar tolv logiska steg för att skapa en bra projektplan, och för projektgenomförandet tekniker för att leda projektet, lämna över resultatet och avsluta projekt
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- Jansson, Tomas, et al.
(author)
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Movement artefact suppression in blood perfusion measurements using a multifrequency technique
- 2002
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In: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:1, s. 69-79
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Journal article (peer-reviewed)abstract
- The standard way of suppressing movement artefacts in Doppler measurements is by means of a high-pass filter. This is because artefacts usually are of high amplitude, but have low frequencies. The immediate drawback is, then, that low-velocity blood flow is also filtered out. In this paper, a method to reduce movement artefacts in blood perfusion measurements is proposed, using simultaneous transmission and reception of multiple frequencies in a continuous-wave Doppler system. It is shown that Doppler signals originating from blood may be considered uncorrelated for a large enough frequency separation between channels, and tissue movements are more correlated. By subtracting perfusion estimates obtained by time-domain processing, correlated signals can be suppressed. The subtraction algorithm is shown to produce a linear perfusion estimate, but with twice the standard deviation compared to an estimate obtained by simply averaging channels. Movement artefacts in both in vitro and in vivo models are shown to be reduced by the algorithm. Imbalance between channels does, however, cause the artefacts to be only partly reduced. The problem can be alleviated by filtering the signals prior to subtraction, but this results in a nonlinear estimate, especially for large time constants in the filter. Some amount of filtering can still be desirable to suppress partly correlated artefacts, even if identical time-domain processing units are implemented, as could be done digitally. (E-mail: tomas.jansson@elmat.lth.se)
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- Jansson, Tomas, 1973-
(author)
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Optimization of sheet metal forming processes
- 2002
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Licentiate thesis (other academic/artistic)abstract
- The aim of the present work is to find a stable and effective optimization algorithm that can be used to determine the location and size of drawbeads in sheet metal forming processes. The result from the optimization will be the restraining force that each drawbead applies to the blank. In addition, optimization has been used to determine the physical dimensions of the drawbead.The study in Paper I is limited to two structures in crashworthiness design, each with two design variables and three responses. The conclusion is that 1.5 times the minimum number of function evaluation should be used to fit the surface approximations. The conclusion of this study gives an indication on how many evaluations that are needed in order to efficiently construct the response surface approximations.Paper II shows that the optimization algorithm using Space Mapping is well suited for optimization problems in crashworthiness design and in the design of sheet metal forming processes. All optimization applications converged to the correct optimum and the computing time was decreased with a maximum of 63% relative to the traditional RSM optimization.The Space Mapping algorithm presented in Paper III converged to an optimum value that is lower than the optimum value from the traditional RSM, when the approximated surfaces from the first RSM iteration were used as the coarse model. The Space Mapping algorithm, however, reached a higher value compared to RSM, when surfaces from the third RSM iteration was used as the coarse model. Hence, the Space Mapping algorithm converged to a better objective value compared to RSM with less evaluations.This thesis has shown that it is possible to apply optimization on the design of sheet metal forming processes. For the problem used in the last paper both the traditional Response Surface Methodology and the Space Mapping technique were successful in avoiding failure due to necking and to decrease the risk of wrinkles. The Response Surface Methodology is robust enough to be used in the industrial tool design process. The Space Mapping technique using linear response surfaces as coarse model needs further research before it can be used efficiently in industry.
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- Jansson, Tomas, et al.
(author)
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Projektledningsmetodik
- 2004
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Book (peer-reviewed)abstract
- Projektledning är numera en yrkesroll i många privata och offentliga professionella verksamheter. Man leder förstås människor i projekt på ungefär samma sätt som människor i andra sammanhang. Men planering och ledarskap i projekt har också vissa särdrag som är gemensamma för alla projekt, men som inte är lika relevanta utanför projekten. Det gör att man kan tala om projekt-ledning, projekt-ledningsmetodik och projekt-ledarskap som begrepp. Projekt genomförs i samspel med en omgivande organisation, vars särdrag har stort inflytande på hur projektet kan ledas. Den här boken gör organisationens projektmiljö begriplig genom att ge ett språk för de viktigaste faktorerna, som t.ex. generella projektroller, affärsbeslut i projekt och projektets indelning i faser, och genom att visa på viktiga skillnader mellan olika typer av projekt.Bokens huvuddel behandlar sedan ingående projektledarens verktyg och tekniker för att definiera, avgränsa, planera, organisera, leda, överlämna och avsluta projektuppgiften. Den förenar de övergripande sammanhangen med praktiskt tillämpbara tekniker som hjälper människor att lyckas med projekt. Projektledningsmetodik är i första hand en lärobok för universitetsstudier och en handbok för den aktive projektledaren, men den passar också för chefer och andra ledare med roller i och kring projekt eller för den som ska delta i projekt-planeringsarbete
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