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Wildman RD, Huntley JM, Hansen JP, Parker DJ. Numerical solution of the Smoluchowski equation for a vibrofluidized granular bed. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:051304. [PMID: 11735915 DOI: 10.1103/physreve.64.051304] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2001] [Indexed: 05/23/2023]
Abstract
A stochastic approach, similar to that used to describe Brownian motion, was used to model the displacement probability of grains in a three-dimensional vibrofluidized granular bed. As neither an analytical description nor measurements of the diffusion coefficients were available, the governing partial differential equation, namely, the Smoluchowski equation, was solved numerically using an iterative procedure, modifying the granular temperature profile at each step. The results of this stochastic model were compared to experimental measurements of the displacement probability density made using positron emission particle tracking. The results indicate that methods based on hard elastic systems such as the Smoluchowski equation are appropriate to granular systems, particularly over timescales greater than the mean collision time.
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Wewer V, Andersen LP, Paerregaard A, Gernow A, Hansen JP, Matzen P, Krasilnikoff PA. Treatment of Helicobacter pylori in children with recurrent abdominal pain. Helicobacter 2001; 6:244-8. [PMID: 11683928 DOI: 10.1046/j.1523-5378.2001.00035.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND The role of Helicobacter pylori remains unclear in children with recurrent abdominal pain (RAP). In this study children with RAP were included in a double blind treatment study to elucidate whether symptoms disappear in children with a H. pylori infection and RAP, if the bacteria are eradicated. METHODS Thirty-seven H. pylori-infected children aged 4.9-14.5 years (median 9.8 years) with RAP were included. H. pylori was identified by histology and culture. The children were treated with amoxicillin and metronidazole for 14 days. A re-endoscopy including biopsies for histology and culture was done at least one month after the end of treatment. Simple questions for symptoms were asked and blood for serology was repeated 3 and 6 months after the end of treatment. During the observation period the results of the re-endoscopy and the serology 3 and 6 months after the re-endoscopy were blinded for 23 patients and opened to 14 of the patients according to the choice of the families. RESULTS The eradication rates were 81% (30/37) in the total group and 74% (17/23) in the blinded group. The IgG antibodies to H. pylori decreased significantly 3 (p =.03) as well as 6 months after end of treatment (p <.001) in children with successful eradication. The number of children with RAP decreased after examination and treatment and the well-being improved after 6 months in almost 95% of the children. However, no correlation was seen between eradication of H. pylori and disappearance of RAP, neither after 3 nor after 6 months' observation in the total group of patients (p =.94 and p =.90) or in the blinded group (p =.42 and p =.65). CONCLUSIONS These results do not provide evidence for a causal relationship between RAP and H. pylori.
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Bolhuis PG, Louis AA, Hansen JP. Many-body interactions and correlations in coarse-grained descriptions of polymer solutions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:021801. [PMID: 11497612 DOI: 10.1103/physreve.64.021801] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2001] [Indexed: 05/23/2023]
Abstract
We calculate the two-, three-, four-, and five-body (state-independent) effective potentials between the centers of mass (c.m.'s) of self-avoiding walk polymers by Monte Carlo simulations. For full overlap, these coarse-grained n-body interactions oscillate in sign as (-1)(n), and decrease in absolute magnitude with increasing n. We find semiquantitative agreement with a scaling theory, and use this to discuss how the coarse-grained free energy converges when expanded to arbitrary order in the many-body potentials. We also derive effective density dependent two-body potentials that exactly reproduce the pair-correlations between the c.m. of the self avoiding walk polymers. The density dependence of these pair potentials can be largely understood from the effects of the density independent three-body potential. Triplet correlations between the c.m. of the polymers are surprisingly well, but not exactly, described by our coarse-grained effective pair potential picture. In fact, we demonstrate that a pair potential cannot simultaneously reproduce the two- and three-body correlations in a system with many-body interactions. However, the deviations that do occur in our system are very small, and can be explained by the direct influence of three-body potentials.
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Hansen JP, McDonald IR. Self-diffusion and electrical conductance in a simple molten salt. ACTA ACUST UNITED AC 2001. [DOI: 10.1088/0022-3719/7/21/002] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Louis AA, Bolhuis PG, Hansen JP. Mean-field fluid behavior of the gaussian core model. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:7961-7972. [PMID: 11138080 DOI: 10.1103/physreve.62.7961] [Citation(s) in RCA: 168] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2000] [Indexed: 05/23/2023]
Abstract
We show that the Gaussian core model of particles interacting via a penetrable repulsive Gaussian potential, first considered by Stillinger [J. Chem. Phys. 65, 3968 (1976)], behaves as a weakly correlated "mean-field fluid" over a surprisingly wide density and temperature range. In the bulk, the structure of the fluid phase is accurately described by the random phase approximation for the direct correlation function, and by the more sophisticated hypernetted chain integral equation. The resulting pressure deviates very little from a simple mean-field-like quadratic form in the density, while the low density virial expansion turns out to have an extremely small radius of convergence. Density profiles near a hard wall are also very accurately described by the corresponding mean-field free-energy functional. The binary version of the model exhibits a spinodal instability against demixing at high densities. Possible implications for semidilute polymer solutions are discussed.
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Hansen JP, Levesque D. The two-dimensional one-component plasma in the hypernetted chain approximation. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/14/21/002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Barrat JL, Baus M, Hansen JP. Freezing of binary hard-sphere mixtures into disordered crystals: a density functional approach. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/20/10/011] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Barrat JL, Hansen JP, Totsuji H. Collective modes and single-particle motion in Yukawa fluids near freezing. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/21/25/003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
This review summarizes and assesses recent theoretical and experimental advances, with special emphasis on the effective interaction between charge-stabilized colloids, in the bulk or in confined geometries, and on the ambiguities of defining an effective charge of the colloidal particles. Some consideration is given to the often neglected discrete solvent effects.
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Louis AA, Bolhuis PG, Hansen JP, Meijer EJ. Can polymer coils Be modeled as "Soft colloids"? PHYSICAL REVIEW LETTERS 2000; 85:2522-2525. [PMID: 10978097 DOI: 10.1103/physrevlett.85.2522] [Citation(s) in RCA: 277] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2000] [Indexed: 05/23/2023]
Abstract
We map dilute or semidilute solutions of nonintersecting polymer chains onto a fluid of "soft" particles interacting via a concentration dependent effective pair potential, by inverting the pair distribution function of the centers of mass of the initial polymer chains. A similar inversion is used to derive an effective wall-polymer potential; these potentials are combined to successfully reproduce the calculated exact depletion interaction induced by nonintersecting polymers between two walls. The mapping opens up the possibility of large-scale simulations of polymer solutions in complex geometries.
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Wildman RD, Huntley JM, Hansen JP, Parker DJ, Allen DA. Single-particle motion in three-dimensional vibrofluidized granular beds. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:3826-3835. [PMID: 11088900 DOI: 10.1103/physreve.62.3826] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2000] [Indexed: 05/23/2023]
Abstract
A technique to probe the interior of three-dimensional dynamic granular systems is presented. Positron emission particle tracking (PEPT) allows a single tracer particle to be followed around a three dimensional vibrofluidized granular bed for periods up to six hours. At present the technique is able to resolve the position of the grains to +/-4 mm, with an average temporal resolution of about 7 ms. Packing fraction profiles are calculated by making use of the ergodicity of the system, and granular temperature profiles are obtained, in the dilute case, from the short time behavior of the mean squared displacement. At longer times, the mean squared displacement shows a range of behavior which can be explained by the presence of strong gradients in the packing fraction. Convection currents were observed, but were sufficiently small in magnitude to be ignored during the analysis of grain motion. The system was modeled using the Smoluchowski equation, which was solved numerically, and the results compared with the experimentally determined displacement probability density functions. Good agreement between experiment and numerical results was achieved using Brownian motion relationships modified to accommodate differences between granular systems and thermal systems.
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Wang JB, Hansen JP, Dubois A. Spin anisotropy for excitation in collisions between two one-electron atoms. PHYSICAL REVIEW LETTERS 2000; 85:1638-1641. [PMID: 10970577 DOI: 10.1103/physrevlett.85.1638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2000] [Indexed: 05/23/2023]
Abstract
The singlet and triplet contributions of excitation cross sections are studied theoretically for collisions between various two one-electron atoms. The spin anisotropy is shown to have a general behavior in the important impact energy range. At low energies triplet cross sections dominate completely over the singlet ones while the opposite is true when the active electron and projectile velocities are comparable. Beyond the matching velocity regime singlet and triplet contributions become identical. We propose a general dynamical interpretation based on the analysis of the time dependency of the electron probability density and probability current density.
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Goulding D, Hansen JP, Melchionna S. Size selectivity of narrow pores. PHYSICAL REVIEW LETTERS 2000; 85:1132-1135. [PMID: 10991492 DOI: 10.1103/physrevlett.85.1132] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2000] [Indexed: 05/23/2023]
Abstract
The selectivity of micropores and ion channels is examined for simple pore topologies within the framework of density functional theory of highly confined fluids. In an infinite cylindrical pore purely steric (excluded volume) effects are shown to lead to strong, nontrivial size selectivity, which is highly sensitive to the pore radius. A crude modeling of electrostatic effects does not alter the relative absorbance of Na+ and K+ ions in a significant way.
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Weile B, Hansen BF, Hägerstrand I, Hansen JP, Krasilnikoff PA. Interobserver variation in diagnosing coeliac disease. A joint study by Danish and Swedish pathologists. APMIS 2000; 108:380-4. [PMID: 10937777 DOI: 10.1034/j.1600-0463.2000.d01-72.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
There is an almost 40-fold difference in incidence rates of symptomatic coeliac disease between Denmark and Sweden. In an attempt to explain this difference, the present study focused on the interobserver agreement when pathologists were assessing small intestinal biopsy specimens from children suspected of suffering from coeliac disease. The study was performed on 90 biopsy specimens from 73 children. Most of the biopsies came from children who turned out not to suffer from coeliac disease after a clinical evaluation including small intestinal biopsy. Using the kappa methodology, the interobserver agreement between two Danish pathologists and one Swedish pathologist, all of whom were experienced, was "moderate" to "substantial" or 0.57-0.75. Kappa indices when the pathologists evaluated selected histological elements were in the interval from 0.24 to 0.67. A comparison of a previous routine diagnostic assessment of the 90 biopsies (14 pathologists) with the results of the experienced pathologists in the present study gave kappa indices of from 0.53 to 0.57. The study could prove no major differences in the histopathological assessment of small intestinal biopsy specimens made by Danish and Swedish pathologists. The difference in clinical presentation of coeliac disease in Denmark and Sweden does not relate to differences in the histopathological assessment of small intestinal biopsies.
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Louis AA, Finken R, Hansen JP. Crystallization and phase separation in nonadditive binary hard-sphere mixtures. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:R1028-R1031. [PMID: 11046530 DOI: 10.1103/physreve.61.r1028] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/1999] [Indexed: 05/23/2023]
Abstract
We calculate for the first time the full phase diagram of an asymmetric nonadditivehard-sphere mixture. The nonadditivity strongly affects the crystallization and the fluid-fluid phase separation. The global topology of the phase diagram is controlled by an effective size ratio y(eff), while the fluid-solid coexistence scales with the depth of the effective potential well.
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Wildman RD, Huntley JM, Hansen JP. Self-diffusion of grains in a two-dimensional vibrofluidized bed. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:7066-75. [PMID: 11970646 DOI: 10.1103/physreve.60.7066] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/1999] [Revised: 07/07/1999] [Indexed: 04/18/2023]
Abstract
The analogy of vibrofluidized granular beds with a thermal gas of hard discs has been tested. Analysis of the mean squared displacement behavior of the grains allowed comparison of the measured diffusion with the predicted value at a particular combination of granular temperature and packing fraction. High speed photography, image analysis, and particle tracking software enabled accurate location of the grains. Appropriate analysis of the three mean squared displacement regimes, ballistic, diffusive, and crossover between the two extremes, allowed both the diffusion coefficient and the granular temperature to be measured at the same packing fraction. Broad agreement between Chapman-Enskog theory relating temperature to self-diffusion and observation was observed up to packing fractions of eta approximately equal to 0.7. At higher packing fractions the grains showed evidence of caging and jump diffusion, with the observed diffusion rapidly diverging from that predicted by theory. Measurement of self-diffusion coefficients and subsequent use of kinetic theory was found to be an accurate method to determine the granular temperature for intermediate packing fractions (eta=0.4-0.6), and would be particularly suitable for those situations where the time resolution of the experimental facility is insufficient to resolve the speed of the grain between collisions.
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Xu H, Hansen JP. Plasma-insulator transition of spin-polarized hydrogen. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:R9-R12. [PMID: 11969868 DOI: 10.1103/physreve.60.r9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/1999] [Indexed: 04/18/2023]
Abstract
A mixed classical-quantum density functional theory is used to calculate pair correlations and the free energy of a spin-polarized hydrogen plasma. A transition to an atomic insulator phase is estimated to occur around r(s)=2.5 at T=10(4) K, and a pressure P is approximately equal to 0.5 Mbar. Spin polarization is imposed to prevent the formation of H2 molecules.
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Bohn J, Hansen JP, Menné T. Ulcerative lichen planus-like dermatitis due to long-term hydroxyurea therapy. J Eur Acad Dermatol Venereol 1998; 10:187-9. [PMID: 9553923 DOI: 10.1111/j.1468-3083.1998.tb00726.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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45
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Hansen JP, Futch DB. Chiropractic services in a staff model HMO: utilization and satisfaction. HMO PRACTICE 1997; 11:39-42. [PMID: 10165554] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Utilization of chiropractic services was assessed in the continuously enrolled, non-Medicaid membership of Group Health Cooperative of South Central Wisconsin in 1993 and 1994. In addition, a random sample of 500 members using chiropractic services in the last quarter of 1994 was surveyed about satisfaction with the services. A total of 5.1% and 5.3% of members used the services in 1993 and 1994, respectively. Highest utilization occurred among women aged 35 to 49, with rates of 9.5% and 9.9%. Satisfaction levels were high in all areas; 95.8% indicated overall satisfaction with chiropractic care and services.
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Kohanoff J, Hansen JP. Statistical properties of the dense hydrogen plasma: An ab initio molecular dynamics investigation. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:768-781. [PMID: 9965124 DOI: 10.1103/physreve.54.768] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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47
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Dijkstra M, Hansen JP, Madden PA. Gelation of a clay colloid suspension. PHYSICAL REVIEW LETTERS 1995; 75:2236-2239. [PMID: 10059248 DOI: 10.1103/physrevlett.75.2236] [Citation(s) in RCA: 107] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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48
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Lock-Andersen J, Hou-Jensen K, Hansen JP, Jensen NK, Søgaard H, Andersen PK. Observer variation in histological classification of cutaneous malignant melanoma. SCANDINAVIAN JOURNAL OF PLASTIC AND RECONSTRUCTIVE SURGERY AND HAND SURGERY 1995; 29:141-8. [PMID: 7569811 DOI: 10.3109/02844319509034330] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To evaluate the variations within and between observers in the interpretation of important histological prognostic factors, a series of 96 melanoma patients was randomly selected from a database of 1691 patients with cutaneous malignant melanoma. The stained sections were examined on two occasions by four experienced pathologists. Analysis by observed agreement and kappa statistics showed maximal tumour thickness to be the best reproducible variable, with ulceration the second best. Regression was the least reproducible, with level of invasion and type of melanoma in the mid range. Intra-observer variation was uniformly less than inter-observer variation for each variable. For tumour thickness a variance component analysis was done to quantify the variability further. The clinician should not base his choice of treatment entirely on the microscopic classification but take into consideration the clinical course and appearance of the tumour.
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Trizac E, Hansen JP. Dynamic scaling behavior of ballistic coalescence. PHYSICAL REVIEW LETTERS 1995; 74:4114-4117. [PMID: 10058419 DOI: 10.1103/physrevlett.74.4114] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Hansen AC, Kristensen IB, Dragsholt C, Hansen JP. [Alcohol, drugs and narcotics in suicides in the Aarhus police district]. Ugeskr Laeger 1995; 157:1524-7. [PMID: 7725551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
For a period of one year all suicides in Aarhus police district were investigated with a view to identifying the presence of alcohol or drugs in the body of the deceased. Fifty-one suicides occurred, 46 of which were examined. One third of the suicides were due to poisoning and one fourth to hanging. Alcohol was detected in 20% and drugs or narcotics were found in approximately 60%. The most frequent findings were benzodiazepines, analgetics, antidepressants and carbon monoxide. Approximately 40% of the deceased had received psychiatric treatment.
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