| 1. |
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| 2. |
- Appelgren, Patrik, et al.
(författare)
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Disruption mechanisms in electrified solid copper jets
- 2011
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
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Tidskriftsartikel (refereegranskat)abstract
- Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.
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| 3. |
- Appelgren, Patrik, et al.
(författare)
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Experimental Study of Electromagnetic Effects on Solid Copper Jets
- 2010
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 77:1, s. 011010-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]
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| 4. |
- Appelgren, Patrik, et al.
(författare)
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Interaction between solid copper jets and powerful electrical current pulses
- 2011
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 78:2
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.
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| 5. |
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| 6. |
- Appelgren, Patrik, et al.
(författare)
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Studies of Electrically-Exploded Conductors for Electric Armour Applications
- 2009
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 115:6, s. 1072-1074
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents experimental studies of current interaction with static copper rods. The results of the static experiments are used to discuss the effects responsible for the disruption of shaped-charge jets in electric armour. These effects include ohmic heating of, and current diffusion into, the rod as well as radial magnetic forces.
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| 7. |
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| 8. |
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| 9. |
- Johansson, Lars Age, et al.
(författare)
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Methodology of studies evaluating death certificate accuracy were flawed.
- 2006
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Ingår i: Journal of Clinical Epidemiology. - : Elsevier BV. - 0895-4356 .- 1878-5921. ; 59:2, s. 125-31
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND OBJECTIVE: Statistics on causes of death are important for epidemiologic research. Studies that evaluate the source data often give conflicting results, which raise questions about comparability and validity of methods. METHODS: For 44 recent evaluation studies we examined the methods employed and assessed the reproducibility. RESULTS: Thirty studies stated who reviewed the source data. Six studies reported reliability tests. Twelve studies included all causes of death, but none specified criteria for identifying the underlying cause when several, etiologically independent conditions were present. We assessed these as not reproducible. Of 32 studies that focussed on a specific condition, 21 provided diagnostic criteria such that the verification of the focal diagnosis is reproducible. Of 16 that discussed the difference between dying "with" and "from" a condition, eight described how competing causes had been handled. For these eight, the selection of a principal cause is reproducible, but in three the selection strategy conflicts with the international instructions issued by the World Health Organization. CONCLUSION: Methods and criteria are often insufficiently described. When described, they sometimes disagree with the international standard. Explicit descriptions of methods and criteria would contribute to methodologic improvement and would allow readers to assess the generalizability of the conclusions.
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| 10. |
- Johansson, Lars Age, 1951-
(författare)
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Targeting Non-obvious Errors in Death Certificates
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mortality statistics are much used although their accuracy is often questioned. Producers of mortality statistics check for errors in death certification but current methods only capture obvious mistakes. This thesis investigates whether non-obvious errors can be found by linking death certificates to hospital discharge data.Data: 69,818 deaths in Sweden 1995. Paper I: Analysing differences between the underlying cause of death from the death certificate (UC) and the main discharge condition from the patient’s last hospitalization (MDC). Paper II: Testing whether differences can be explained by ICD definitions of UC and MDC. Paper III: Surveying methods in 44 current studies on the accuracy of death certificates. Paper IV: Checking death certificates against case summaries for: i) 573 deaths where UC and MDC were the same or the difference could be explained; ii) 562 deaths where the difference could not be explained.Results: In 54% of deaths the MDC differed from the UC. Almost two-thirds of the differences were medically compatible since the MDC might have developed as a complication of the UC. Of 44 recent evaluation studies, only 8 describe the methods in such detail that the study could be replicated. Incompatibility between MDC and UC indicates a four-fold risk that the death certificate is inaccurate. For some diagnostic groups, however, death certificates are often inaccurate even when the UC and MDC are compatible.Conclusion: Producers of official mortality statistics could reduce the number of non-obvious errors in the statistics by collecting additional information on incompatible deaths and on deaths in high-risk diagnostic groups. ICD conventions contribute to the quality problem since they presuppose that all deaths are due to a single underlying cause. However, in an ageing population an increasing number of deaths are due to an accumulation of etiologically unrelated conditions.
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| 11. |
- Johansson, Lars Age, et al.
(författare)
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Unexplained differences between hospital and mortality data indicated mistakes in death certification : an investigation of 1,094 deaths in Sweden during 1995
- 2009
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Ingår i: Journal of Clinical Epidemiology. - : Elsevier BV. - 0895-4356 .- 1878-5921. ; 62:11, s. 1202-1209
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Mortality statistics are important for epidemiological research. We examine if discrepancies between death certificate (DC) and hospital discharge condition (HDC) indicate certification errors. STUDY DESIGN AND SETTING: From 39,872 hospital deaths in Sweden in 1995, we randomly selected 600 "cases," where DC and HDC were incompatible, and 600 compatible "controls," matched on sex, age, and underlying cause of death. We obtained case summaries for 1,094 (91%) of these. Using a structured protocol, we assessed the accuracy of DCs. RESULTS: Regression analysis indicated diagnostic group and "case" or "control" as the variables that most affected the accuracy. Malignant neoplasm "controls" had the highest accuracy (92%), and benign and unspecified tumor "cases," the lowest (20%). For all diagnostic groups except one, compatible "controls" had better accuracy than incompatible "cases." The exception, chronic obstructive lung disease, had low accuracy for both "cases" (54%) and "controls" (52%). CONCLUSION: Incompatibility between DC and HDC indicates a greater risk of certification errors. For some diagnostic groups, however, DCs are often inaccurate even when DC and HDC are compatible. By requesting additional information on incompatible cases and all deaths in high-risk diagnostic groups, producers of mortality statistics could improve the accuracy of the statistics.
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| 12. |
- Kunkel, Stefan, 1975-
(författare)
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Quality Management in Hospital Departments : Empirical Studies of Organisational Models
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general aim of this thesis was to empirically explore the organisational characteristics of quality systems of hospital departments, to develop and empirically test models for the organisation and implementation of quality systems, and to discuss the clinical implications of the findings. Data were collected from hospital departments through interviews (n=19) and a nation-wide survey (n=386). The interviews were analysed thematically and organisational models were developed. Relationships among aspects of organisation and implementation were hypothesised and analysed with structural equation modelling. The result was a new framework with three organisational aspects of quality systems each with two sub-aspects: structure (resources and administration), process (culture and cooperation), and outcome (evaluation of goal achievement and development of competence). Strong positive relationships were confirmed among structure, process, and outcome. Quality systems could therefore be classified into three organisational degrees. For instance, quality systems of high organisational degree often had adequate resources and administration as well as positive organisational cultures and high cooperation among different professions. Advanced designs required quality systems of high organisational degrees. Examples of such designs were coordination between departments, random check ups, and accreditation. The organisationally demanding quality systems had been implemented through cooperative implementation, that is, directed by managers while at the same time giving opportunities for staff to participate in planning and designing. The results can be useful to managers, quality coordinators, and clinicians when they describe, develop, implement, and evaluate the effectiveness and efficiency of quality systems in hospital departments.
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| 13. |
- Lundberg, Patrik, et al.
(författare)
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Influence of scale on the penetration of tungsten rods into steel-backed alumina targets
- 1996
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 18:4, s. 403-416
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Tidskriftsartikel (refereegranskat)abstract
- As ballistic tests are often performed in reduced geometrical scale, the scaling laws are important for the interpretation of the results. In this study, we tested the validity of replica scaling, by which we mean that all geometrical dimensions are scaled uniformly, while the materials and the impact velocity are kept the same. Long tungsten projectiles with length-to-diameter ratio 15 were fired against unconfined alumina targets with steel backing. The tests were carried out with impact velocities 1500 m s−1 and 2500 m s−1, and in three different scales with projectile lengths 30, 75 and 150 mm (diameters 2, 5 and 10 mm). The alumina targets were photographed by means of a high-speed camera, and the tungsten projectiles were photographed inside the alumina targets by means of flash radiography. Also, the residual penetrations in the steel backings were measured. The Johnson-Holmquist model for ceramic materials was implemented into the AUTODYN code, which was used for simulation of the experiments. The agreement between results of experiment and simulation was fair, and over the tested interval of scales replica scaling was found to be valid with reasonable accuracy.
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| 14. |
- Schrage, Benedikt, et al.
(författare)
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Lower socioeconomic status predicts higher mortality and morbidity in patients with heart failure
- 2021
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Ingår i: Heart. - : BMJ PUBLISHING GROUP. - 1355-6037 .- 1468-201X. ; 107:3, s. 229-236
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Tidskriftsartikel (refereegranskat)abstract
- Objective It is not fully understood whether and how socioeconomic status (SES) has a prognostic impact in patients with heart failure (HF). We assessed SES and its association with patient characteristics and outcomes in a contemporary and well-characterised HF cohort. Methods Socioeconomic risk factors (SERF) were defined in the Swedish HF Registry based on income (low vs high according to the annual median value), education level (no degree/compulsory school vs university/secondary school) and living arrangement (living alone vs cohabitating). Results Of 44 631 patients, 21% had no, 33% one, 30% two and 16% three SERF. Patient characteristics strongly and independently associated with lower SES were female sex and no specialist referral. Additional independent associations were older age, more severe HF, heavier comorbidity burden, use of diuretics and less use of HF devices. Lower SES was associated with higher risk of HF hospitalisation/mortality, and overall cardiovascular and non-cardiovascular events. These associations persisted after extensive adjustment for patient characteristics, treatments and care. The magnitude of the association increased linearly with the increasing number of coexistent SERF: HR (95% CI) 1.09 (1.05 to 1.13) for one, 1.16 (1.12 to 1.20) for two and 1.22 (1.18 to 1.28) for three SERF (p<0.01). Conclusions In a contemporary and well-characterised HF cohort and after comprehensive adjustment for confounders, lower SES was linked with multiple factors such as less use of HF devices and age, but most strongly with female sex and lack of specialist referral; and associated with greater risk of morbidity/mortality.
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| 15. |
- Westerling, Lars, 1943-
(författare)
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Interaction of Cylindrical Penetrators with Ceramic and Electromagnetic Armour
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Armoured vehicles have traditionally used steel armour as protection against penetrators such as projectiles and shaped charge jets. The latter produce a thin stretching metal jet, usually of copper, with a tip velocity of about 7-8 km/s. In order to obtain more weight-efficient solutions, there is a search for lighter materials and other protection techniques. In this thesis, ceramic and electromagnetic armours are studied. Ceramic materials are lighter than steel, and their high compressive strength makes them useful as armour materials. Electromagnetic armour consists of two metal plates connected to an electric power supply capable of delivering a strong current pulse. A conductive penetrator passing through both plates is destroyed by the effects of the resulting current.Tests of the ceramic armour materials alumina and boron carbide were performed with reverse impact technique, which signifies that a target assembly (ceramic confined in a metal cylinder) was launched by a gun towards a projectile placed in front of the gun barrel. By this technique yaw was eliminated, but the geometric scale had to be very small. Therefore, we studied scaling laws for ceramic armour through a series of tests with direct impact technique and projectile diameters from 2 to 10 mm. The small scale has the advantage that flash X-ray photography can be used to photograph the projectile inside the ceramic target. The phenomenon of interface defeat or dwell was also demonstrated. It signifies that the ceramic, at least for a short time, can withstand the impact pressure so that the projectile just flows out onto the target surface. A transition velocity, above which dwell does not occur, was determined. Simulations were performed with the continuum-dynamic code Autodyn and by use of a model for the brittle ceramic materials by Johnson and Holmquist. The simulations reasonably well represented the penetration behaviour above the transition velocity. They also did below, if under this condition the ceramic model was forced to remain undamaged.The performance of electromagnetic armour was tested against a shaped charge jet. The jet was registered with shadowgraph flash X-ray photography between the plates and after passing through the plates. The current through the jet and the voltage over the plates were also registered. The current caused heating leading to melting and even vaporization. The magnetic Lorentz force compressed the jet radially, and as this effect increases with decreasing jet radius, instability may arise. Explosions in the compressed regions resulted in a fragmented jet with disk-shaped fragments which are less effective penetrators than the elongated fragments obtained in the absence of current. We also performed a theoretical study, in which the penetrator was subjected to small elastic strains only and the current was constant. The magnetic field was determined by FFT, and the stresses due to the Lorentz force were calculated with a semi-analytical method. The velocity skin effect was demonstrated.
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| 16. |
- Westerling, Lars, et al.
(författare)
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Stresses in a long cylindrical conductor moving axially through a pair of electrode plates under stationary conditions
- 2013
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 80:2, s. 021013-
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Tidskriftsartikel (refereegranskat)abstract
- In a conductor carrying electric current, the Lorentz force gives rise to mechanical stresses. Here, we study a long elastic cylindrical conductor that moves axially with constant velocity through two electrode plates. The aims are to explore how the stresses in the conductor depend on the velocity in the stationary case of constant current and to assess the validity of the analytic method used. The diffusion equation for the magnetic flux density is solved by use of Fourier transform, and the current density is determined. The stresses, due to the Lorentz force, are found by use of an analytic method combining the solutions of a quasi-static radial problem of plane deformation and a dynamic axial problem of uniaxial stress. They are also determined through FE analysis. Radial field profiles between the plates indicate a velocity skin effect signifying that the current and the magnetic field are concentrated near the cylindrical surface up-stream and are more uniformly distributed downstream. The radial and hoop stresses are compressive, while the axial stress is tensile. The von Mises effective stress increases towards the symmetry axis, in the downstream direction, and with velocity. There are circumstances under which a large current can produce an effective stress in a copper conductor of the order of the yield stress without causing a significant temperature rise. The stresses obtained with the two methods agree well, even relatively near the electrode plates. The analytical method should be useful in similar cases as well as for the provision of test cases for more general simulation tools.
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| 17. |
- Westerling, Lars, et al.
(författare)
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Tungsten long-rod penetration into confined cylinders of boron carbide at and above ordnance velocities
- 2001
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Ingår i: International Journal of Impact Engineering. - 0734-743X .- 1879-3509. ; 25:7, s. 703-714
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Tidskriftsartikel (refereegranskat)abstract
- The purpose was to investigate the influence of impact velocity and confinement on the resistance of boron carbide targets to the penetration of tungsten long-rod projectiles. Experimental tests with impact velocities from 1400 to 2600 m/s were performed using a two-stage light-gas gun and a reverse impact technique. The targets consisted of boron carbide cylinders confined by steel tubes of various thicknesses. Simulations were carried out using the AUTODYN-2D code and Johnson–Holmquist's constitutive model with and without damage evolution. The experimental results show that the penetration process had different character in three different regions. At low-impact velocities, no significant penetration occurred. At high-impact velocities, the relation between penetration velocity and impact velocity was approximately linear, and the penetration was steady and symmetrical. In between, there was a narrow transition region of impact velocities with intermittent and strongly variable penetration velocity. In the lower part of this region, extended lateral flow of the projectile took place on the surface of the target. The influence of confinement on penetration velocity was found to be small, especially at high-impact velocities. The simulated results for penetration velocity versus impact velocity agreed fairly well with the experimental results provided damage evolution was suspended below the transition region.
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