| 291. |
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| 292. |
- Aare, Magnus, et al.
(författare)
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Evaluation of head response to ballistic helmet impacts using the finite element method
- 2007
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Ingår i: International Journal of Impact Engineering. - : Elsevier BV. - 0734-743X .- 1879-3509. ; 34:3, s. 596-608
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Tidskriftsartikel (refereegranskat)abstract
- Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops' (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.
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| 293. |
- Aare, Magnus, et al.
(författare)
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Injuries from motorcycle- and moped crashes in Sweden from 1987 to 1999.
- 2003
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Ingår i: Injury control and safety promotion. - : Informa UK Limited. - 1566-0974 .- 1744-4985. ; 10:3, s. 131-8
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to study injuries from motorcycle and moped crashes in Sweden from 1987 to 1999. Databases at the National Board for Health and Welfare and codes from both ICD9 and ICD10 systems were used, including patterns of age, gender, E-code and type of injury. Length of hospital stay, type of injuries and trends over time was evaluated. To get a more detailed picture of the age distribution, type of vehicle used and number of killed, data from the Swedish National Road Administration were also used. In Sweden, 27,122 individuals received in-patient care due to motorcycle and moped injuries between 1987 and 1999. The motorcycle and moped injury rate was reduced in the second half of the studied period and so were the total days of treatment per year. Males had eight times the incidence of injuries compared to females. Riders under the age of 26 and in particular those at an age of 15 had the highest incidence rate. Head injuries were the most frequent diagnosis, followed by fractures to the lower limbs. Concussion was the most frequent head injury. Focal and diffuse brain injuries combined showed the same frequency as concussion. It is concluded that more preventative strategies must be presented before the injury rate can be reduced.
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| 294. |
- Aare, Magnus, et al.
(författare)
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Injury tolerances for oblique impact helmet testing
- 2004
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Ingår i: International Journal of Crashworthiness. - : Informa UK Limited. - 1358-8265 .- 1754-2111. ; 9:1, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- The most frequently sustained severe injuries in motorcycle crashes are injuries to the head, and many of these are caused by rotational force. Rotational force is most commonly the result of oblique impacts to the head. Good testing methods for evaluating the effects of such impacts are currently lacking. There is also a need for improving our understanding of the effects of oblique impacts on the human head. Helmet standards currently in use today do not measure rotational effects in test dummy heads. However rotational force to the head results in large shear strains arising in the brain, which has been proposed as a cause of traumatic brain injuries like diffuse axonal injuries (DAI). This paper investigates a number of well-defined impacts, simulated using a detailed finite element (FE) model of the human head, an FE model of the Hybrid III dummy head and an FE model of a helmet. The same simulations were performed on both the FE human head model and the FE Hybrid III head model, both fitted with helmets. Simulations on both these heads were performed to describe the relationship between load levels in the FE Hybrid III head model and strains in the brain tissue in the FE human head model. In this study, the change in rotational velocity and the head injury criterion (HIC) value were chosen as appropriate measurements. It was concluded that both rotational and translational effects are important when predicting the strain levels in the human brain.
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| 295. |
- Aare, Magnus, 1974-
(författare)
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Prevention of Head Injuries - focusing Specifically on Oblique Impacts
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The massive number of injuries sustained in trafficaccidents is a growing problem worldwide, especially indeveloping countries. In 1998, more than one million peoplewere killed in traffic accidents worldwide, while about tentimes as many people were injured. Injuries to the centralnervous system and in particular to the headare especiallycritical to human life. This thesis contains five researchpapers looking at head injuries and head protection, proposingnew and more efficient ways of protecting the head, especiallyin traffic accidents.In order to define the national dimensions of the patternsof injuries incurred in motorcycle and moped accidents inSweden, a statistical survey was performed on data spanning a13-year period (Paper A). In Sweden, 27,100 individualsreceived in-patient care for motorcycle and moped accidentinjuries between 1987 and 1999. The motorcycle and moped injuryrate reduced in the second half of the study period, so toowere the total number of days of treatment per year. Males hadeight times the incidence of injuries of females. Head injurieswere the single most frequent diagnosis, followed by fracturesof the lower limbs. Concussion was the most frequent headinjury. These statistics clearly show the need for better headinjury prevention systems.According to the statistics, the most common type of impactto the head in motorcycle and moped accidents is an obliqueimpact. Oblique impacts generate rotations of the head, whichare a common cause of the most severe head injuries. Thereforea new test rig was constructed to reproduce oblique impacts toa helmeted dummy head, simulating those occurring in real lifeaccidents (Paper B). The new test rig was shown to provideuseful data at speeds of up to 50 km/h and with impact anglesvarying from purely tangential to purely radial. Thisinnovative test rig appears to provide an accurate method formeasuring accelerations in oblique impacts to helmets.When testing the performances of motorcycle helmets,discrepancies are usually seen in the test results. In order toevaluate these discrepancies, the finite element method (FEM)was used for simulations of a few oblique helmet impacts (PaperC). Amongthe parameters studied, the coefficients of frictionbetween the impacting surface and the helmet and between thehead and the helmet had the most significant influence on therotational accelerations. Additionally, a thinner andconsequently also weaker shell and a weaker liner, providedbetter protection for the impacts studied.Since there are no generally accepted global injurythresholds for oblique impacts to the human head, a study wasdesigned to propose new injury tolerances accounting for bothtranslations and rotations of the head (Paper D). In thatstudy, FE models of (a) a human head, (b) a Hybrid III dummyhead, and (c) the experimental helmet were used. Differentcriteria were proposed for different impact scenarios. Both thetranslational and the rotational effects were found to beimportant when proposing a predictor equation for the strainlevels experienced by the human brain in simulated impacts tothe head.In order to reduce the level of head injuries in society andto better understand helmet impacts from different aspect, aballistic impact was also studied (Paper E). The effects ofdifferent helmet shell stiffness and different angles ofimpacts were simulated. In this study, the same FE head modelfrom Paper D was used, however here it was protected with amodel of a composite ballistic helmet. It was concluded thatthe helmet shell should be stiff enough to prevent the insideof the shell from striking the skull, and that the strainsarising in the brain tissue were higher for some obliqueimpacts than for purely radial ones.In conclusion, this thesis describes the injury pattern ofmotorcycle and moped accidents in Sweden. This thesis showsthat the injuries sustained from these accidents can bereduced. In order to study both translational as well asrotational impacts, a new laboratory test rig was designed. Byusing the finite element method, it is possible to simulaterealistic impacts to the head and also to predict how severehead injuries may potentially be prevented.
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| 296. |
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| 297. |
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| 298. |
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| 299. |
- Aarebrot, Frank, 1947-, et al.
(författare)
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Statehood, Secularisation, Cooperation : Explaining Democratic Survival in Inter-War Europe - Stein Rokkan's Conceptual Map Revisited
- 1995
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Ingår i: Historical social research / Historische Sozialforschung. - Köln : Zentrum für historische Sozialforschung. - 0172-6404. ; 20:2, s. 210-225
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses itself to the crisis of democracy in inter-war Europe which saw the breakdown of one democratic regime after the other with Czechoslovakia as the only survivor case in Eastern and Central Europe by the end of this period. It is cast within the framework of Stein Rokkan's seminal conceptual map of Europe which is expanded in order to account for countries and variables originally not included in his analytical scheme. The analysis leads to the following conclusion: where the state building was weak and the legacy of empire strong, or where secular nation building was still impaired by deeply rooted religious sentiments, or where significant segments representing major cleavages where not coopted into a constitutional compromise, the chances for democratic survival in inter-war Europe were slim indeed. The conclusion applies to the inter-war era alone, but it clearly has implications for contemporary Europe. Noting that statehood and secularization ranked high on the agenda of communist Eastern Europe, the authors raise the paradoxical question if the success of democracy in this part of the world may in fact be a byproduct of the extent to which the now defunct communist regimes were successful in promoting their pet goals.
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| 300. |
- Aarebrot, Frank, 1947-, et al.
(författare)
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The View from EFTA
- 1998
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Ingår i: Public Opinion and Internationalized Governance. - Oxford : Oxford University Press. - 9780198294764 ; , s. 344-367
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter examines public opinion regarding European Community integration in the five small but comparatively prosperous countries in the European Free Trade Association (EFTA). The evidence reveals a split. On the one hand, there is the positive endorsement expressed in Austria, Finland and Sweden; on the other, there is the negative assessment expressed in Norway and Switzerland. This ambivalence confirms that the impact of centre-periphery location is complex. Moreover, as the Norwegian and Swiss cases indicate, the centre-periphery cleavage within countries is as relevant as that between countries to an understanding of support for internationalized governance.
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