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J P Hansen

Publications and source records attributed to J P Hansen.

At least 19 recordsLinked to original sources
PubMed2003

Nonmonotonic variation with salt concentration of the second virial coefficient in protein solutions.

The osmotic virial coefficient B2 of globular protein solutions is calculated as a function of added salt concentration at fixed pH by computer simulations of the "primitive model." The salt and counterions as well as a discrete charge pattern on the protein surface are explicitly incorporated. For parameters roughly corresponding to lysozyme, we find that B2 first decreases with added salt concentration up to a threshold concentration, then increases to a maximum, and then decreases again upon further raising the ionic strength. Our studies demonstrate that the existence of a discrete charge pattern on the protein surface profoundly influences the effective interactions and that linear and nonlinear Poisson Boltzmann theories fail for large ionic strength. The observed nonmonotonicity of B2 is compared with experiments. Implications for protein crystallization are discussed.

Journal Article↗
PubMed2002

Excitation in ion-atom collisions inside subfemtosecond laser pulses.

We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions.

Journal Article↗
PubMed2001

[Relatives' attitude towards death in hospital].

INTRODUCTION: A survey was conducted over 13 months to measure the satisfaction level of relatives to patients, who had died in hospital. METHODS: The survey contained a questionnaire of 75 questions measuring satisfaction in different areas: the amount and quality of information given to the relatives by doctors, the support and care provided by the staff, and the quality of the physical environment. RESULTS: Out of 619 questionnaires posted, 462 were returned (74.6% response rate). Only half the relatives were satisfied with the level of information given by doctors to themselves and the one dying. Twenty-four per cent of the respondents were dissatisfied by the length of time taken by doctors to inform them about the situation. A broad majority of respondents (85%) were very satisfied with the care and support provided by the nursing staff. Sixty-six per cent of the patients died in private wards. Fifty-five per cent of the relatives were satisfied with the quality of the patient's room, but only 37% were satisfied with the environment offered to them. One in five was especially dissatisfied by the lack of a special room, which would permit enabling private conversations in an undisturbed environment. DISCUSSION: Our survey shows that doctors' communication with the relatives of dying patients needs to be improved. There also seems to be a need for providing a better environment for the relatives of dying patients by reserving separate rooms for rest and conversation.

Attitude to Death↗
PubMed2001

Numerical solution of the Smoluchowski equation for a vibrofluidized granular bed.

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.

Journal Article↗
PubMed2001

Many-body interactions and correlations in coarse-grained descriptions of polymer solutions.

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.

Journal Article↗
PubMed2001

Treatment of Helicobacter pylori in children with recurrent abdominal pain.

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.

Abdominal Pain↗
PubMed2000

Size selectivity of narrow pores.

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.

Ion Channels↗
PubMed2000

Interobserver variation in diagnosing coeliac disease. A joint study by Danish and Swedish pathologists.

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.

Adolescent↗
PubMed2000

Effective interactions between electric double layers.

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.

Journal Article↗
PubMed1999

Self-diffusion of grains in a two-dimensional vibrofluidized bed.

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.

Journal Article↗
PubMed1999

Plasma-insulator transition of spin-polarized hydrogen.

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.

Journal Article↗
PubMed1997

Chiropractic services in a staff model HMO: utilization and satisfaction.

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.

Adult↗
PubMed1995

[Alcohol, drugs and narcotics in suicides in the Aarhus police district].

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.

Adult↗
PubMed1995

Observer variation in histological classification of cutaneous malignant melanoma.

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.

Analysis of Variance↗
PubMed1994

Helicobacter pylori infection in children with recurrent abdominal pain.

Helicobacter pylori was cultured and Helicobacter-like organisms (HLO) were seen in 6 (16%) of 37 children with recurrent abdominal pain. Five children had concomitant histological inflammation, but none had endoscopic changes. All 6 children demonstrated positive serology. Compared with the total group, they were more often from developing countries, larger families and lower social groups. Treatment with phenoxymethyl penicillin and colloidal bismuth subcitrate did not result in side effects or elevated serum levels of serum bismuth. Three children demonstrated metronidazole-resistant strains and the treatment of these children remained an unsolved problem. Among the 31 H. pylori/HLO negative children 8 (26%) demonstrated histological changes, 5 (16%) endoscopic changes and 11 (35%) had positive serology. In conclusion, pathological findings at upper gastrointestinal endoscopy are common in children with recurrent abdominal pain. Because of disconcordance between endoscopy, histology and culture, we recommend that biopsies should always be taken to clarify the diagnosis.

Abdominal Pain↗
PubMed1994

The humoral immune response to Helicobacter pylori infection in children with recurrent abdominal pain.

The systemic humoral immune response to Helicobacter pylori antigens was investigated in 36 children with recurrent abdominal pain (RAP). H. pylori was cultured and Helicobacter-like organisms (HLO) were seen in six children, three of whom had active and two inactive chronic gastritis. None of these children had endoscopic abnormalities. All sex children had increased IgG antibodies to heat-stable H. pylori antigens which were of the IgG1 and IgG3 subclasses. Using six other IgG tests, four of which were commercially available, two to five H. pylori-positive children were found seropositive. Five of six H. pylori-negative children with inactive chronic gastritis and no endoscopic abnormalities had increased IgM antibody levels in addition to increased or borderline increased IgG antibody levels to H. pylori, indicating activity in a chronic H. pylori infection. Five children without H. pylori and with no morphological changes, but with gastritis or duodenitis by endoscopy, had significantly lower IgG and IgA antibody levels compared to other groups. Six of nineteen children without H. pylori, and with no morphological or endoscopic changes had increased IgG and IgM antibody levels to H. pylori. All H. pylori-negative children were seronegative by the four commercial kits. Overall, 12 (33%) of 36 children with RAP were either H. pylori positive by culture and microscopy or had increased IgG antibody levels to H. pylori, which is significantly different from the 10-14% seropositive rate of asymptomatic children. H. pylori may therefore be a cause of RAP in one quarter to one third of the children with RAP in whom other etiologies of RAP are excluded. Further studies on a large number of children are needed for an extended evaluation of the humoral immune response to H. pylori and for further examination of commercial kits which seem to give a high number of false-negative results.

Abdominal Pain↗
PubMed1993

After Reykjavik.

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Arctic Regions↗