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Biomedical subjects

N Christensen

Publications and source records attributed to N Christensen.

At least 19 recordsLinked to original sources
PubMed2005

Upper limits on a stochastic background of gravitational waves.

The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.

Journal Article↗
PubMed2005

Limits on gravitational-wave emission from selected pulsars using LIGO data.

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.

Journal Article↗
PubMed2004

Removal of polycyclic aromatic hydrocarbons (PAHs) from sewage sludge by anaerobic degradation.

Due to the hydrophobic nature of the polyaromatic hydrocarbons (PAHs) they are mostly bound to the sludge and escape aerobic treatment in a wastewater treatment plant. They therefore proceed directly to the anaerobic post treatment, terminate in the sludge, and can be released to the environment if land spreading is used. PAH degradation in anaerobic methanogenic systems has only recently been shown to occur. In this study we have assessed several factors of anaerobic PAH degradation by evaluating thermodynamic feasibility of degradation, assessing degradation at different temperatures, and investigating the enriched cultures using fluorescent in-situ hybridization (FISH). Thermodynamic calculations indicated that PAH degradation was possible under methanogenic conditions, in the presence of hydrogen utilizing methanogens. Removal of naphthalene and 1-methyl naphthalene depended both on temperature and the initial inoculum. Inocula sourced from contaminated land sites were the most effective. The enrichments were all a mixture of Bacteria, and Archaea, and the Archaea were generally identified as Methanobacteriales, using an order-specific probe. The bacteria were not specifically identified. The results indicate a syntrophic culture, with the bacteria oxidizing the naphthalene, and the Archaea converting the hydrogen produced by oxidation, to methane.

Bacteria, Anaerobic↗
PubMed2000

Spontaneous regression of CIN and delayed-type hypersensitivity to HPV-16 oncoprotein E7.

We investigated delayed-type hypersensitivity to human papillomavirus (HPV) in women with cervical dysplasia or cancer. Women were challenged by skin tests with synthetic HPV-16 E7 oncoprotein peptides. 11 women were regressors (cleared disease without treatment) and 37 were progressors (required surgery). Antibodies to early antigens (markers for progression) were detectable in a higher proportion of cancer patients than all other patients, particularly progressors with cervical intraepithelial neoplasia (CIN). By contrast, cellular immunity to HPV-16 E7, measured by skin test, was significantly (p=0.0001) associated with clinical and cytological resolution of HPV-induced CIN, indicating that E7-specific T-helper cells have a role in control of HPV.

Female↗
PubMed2000

Specific serum IgG, IgM and IgA antibodies to human papillomavirus types 6, 11, 16, 18 and 31 virus-like particles in human immunodeficiency virus-seropositive women.

To evaluate the humoral immune response to human papillomavirus (HPV) in women infected with human immunodeficiency virus (HIV), serum samples of 83 HIV-positive individuals were analysed by ELISA for specific antibodies of the isotypes IgG, IgA and IgM recognizing HPV-6, -11, -16, -18 and -31 L1 virus-like particles (VLPs). Papillomavirus-related lesions were present in 30 of 83 HIV-positive women. Twenty-one women (25%) presented with high-/intermediate-grade anogenital squamous intraepithelial lesions. PCR analysis and sequencing for HPV typing was done from biopsy specimens of 18 women; PCR-positive results were obtained in 90% of cases. In addition, HPV DNA hybrid capture assays were performed from cervical swabs of 58 HIV-positive women, 53% of whom had a positive result for high-risk HPV. Overall, positive IgG reactivity to HPV-6/-11 and HPV-16/-18/-31 was seen in 19%/31% and 49%/30%/24% of HIV-positive women, respectively. HPV-seropositivity was even higher than in 48 HIV-negative cervical intraepithelial neoplasia/cancer patients with percentages as follows: 8%/2% and 31%/15%/15%. This difference was significant for HPV-16 (P=0.046). IgA responses were comparable to IgG. IgM responses were low. The extraordinarily high rate of antibodies to the capsid protein L1 of high-risk HPVs (HPV-16, -18 and/or -31) in 58% of HIV-positive women compared to 19% (P=0.00001) of 102 healthy HIV-negative control women suggests a high lifetime cumulative exposure to HPV and increased expression of capsid proteins due to cellular immunodeficiency in HIV-infected women.

Adult↗
PubMed2000

Numerical investigation of the effects of classical phase space structure on a quantum system with decoherence

We present a detailed numerical study of a chaotic classical system and its quantum counterpart. The system is a special case of a kicked rotor and for certain parameter values possesses cantori dividing chaotic regions of the classical phase space. We investigate the diffusion of particles through a cantorus. A quantum analysis confirms that the cantori act as barriers. We numerically estimate the classical phase space flux through the cantorus per kick and relate this quantity to the behavior of the quantum system. We introduce decoherence via environmental interactions with the quantum system and observe the subsequent increase in the transport of quantum particles through the boundary.

Journal Article↗
PubMed2000

Momentum distributions for the quantum delta-kicked rotor with decoherence

We report on the momentum distribution line shapes for the quantum delta-kicked rotor in the presence of environment induced decoherence. Experimental and numerical results are presented. In the experiment ultracold cesium atoms are subjected to a pulsed standing wave of near resonant light. Spontaneous scattering of photons destroys dynamical localization. For the scattering rates used in our experiment the momentum distribution shapes remain essentially exponential.

Journal Article↗
PubMed2000

Bayesian reconstruction of chaotic dynamical systems

We present a Bayesian approach to the problem of determining parameters of nonlinear models from time series of noisy data. Recent approaches to this problem have been statistically flawed. By applying a Markov chain Monte Carlo algorithm, specifically the Gibbs sampler, we estimate the parameters of chaotic maps. A complete statistical analysis is presented, the Gibbs sampler method is described in detail, and example applications are presented.

Journal Article↗
PubMed2000

Development of a long-term ascending urinary tract infection mouse model for antibiotic treatment studies.

A model of ascending unobstructed urinary tract infection (UTI) in mice was developed to study the significance of the antibiotic concentration in urine, serum, and kidney tissue for efficacy of treatment of UTI in general and pyelonephritis in particular. Outbred Ssc-CF1 female mice were used throughout the study, and Escherichia coli was used as the pathogen. The virulence of 11 uropathogenic E. coli isolates and 1 nonpathogenic laboratory E. coli strain was examined. Strain C175-94 achieved the highest counts in the kidneys, and this strain was subsequently used as the infecting organism. The model gave reproducible bladder infections, i.e., bacteria were recovered from 22 of 23 control mice after 3 days, and histological examination of kidney tissue showed that of 14 infected kidneys, 7 (50%) showed major histological changes, whereas 3 of 36 uninfected kidneys showed major histological changes (P = 0.018). Once the model was established, the efficacies of different doses of cefuroxime and gentamicin, corresponding to active concentrations in urine only or in urine, serum, and kidney tissue simultaneously, were examined. All cefuroxime doses resulted in significantly lower counts in urine than control treatments, but the dose which produced concentrations of cefuroxime only in urine and not in serum or kidney tissue had no effect on kidney infection. Even low doses of gentamicin (0.05 mg/mouse) resulted in concentrations in renal tissue for prolonged times due to accumulation. All gentamicin doses had a significant effect (compared to the effect of the control treatment) on bacterial counts in urine and kidneys. The antibiotic effect on bacterial counts in bladders was negligible for unknown reasons. Use of the mouse UTI model is feasible for study of the effect of an antibiotic in the urinary system, although the missing antibacterial effect in the bladder needs further evaluation.

Animals↗
PubMed1999

Capture ElISA and in vitro cell binding assay for the detection of antibodies to human papillomavirus type 6b virus-like particles in patients with anogenital warts.

To investigate human papillomavirus (HPV) virus-like particle (VLP)-specific antibody responses among anogenital warts patients, a VLP-based capture ELISA was established. Twenty-six percent (35/134) of control subjects and 50.0% (39/78) of patients with current anogenital warts showed IgG seropositivity to HPV 6b VLPs. HPV 6b VLP-specific antibody responses recognised native VLPs only, and had no cross-reaction with HPV type 16 VLPs. No differences in reactivity were observed between L1 and L1 + L2 VLPs, suggesting that L2 contributes little to the total immunogenicity of the papillomavirus virion. A VLP-cell binding assay was also established. Some sera from patients with anogenital warts specifically inhibited VLP binding to the surface of epithelial cells, suggesting that these antibodies might be functionally neutralising. These data show that serological responses to HPV 6b VLPs were induced among some but not all patients with anogenital warts, and give a proportional estimate of infection in the community.

Adolescent↗
PubMed1997

A monoclonal antibody against intact human papillomavirus type 16 capsids blocks the serological reactivity of most human sera.

A type-specific and neutralizing mouse MAb (V5) against human papillomavirus (HPV) type 16 capsids was found to block the serological reactivity of human sera with the corresponding capsids. Out of 352 human serum samples tested for the presence of IgG against HPV-16, more than 75% of reactive sera were completely blocked by the V5 antibody. Type-specific MAbs against HPV-6, -18 and -33 were also found to block serological reactivity with capsids of the corresponding HPV types for the majority of reactive human sera. The results suggest that most antibodies in human sera that are reactive with intact HPV capsids recognize the same or closely related major antigenic determinant(s).

Adolescent↗
PubMed1996

Cancer among Circumpolar Inuit 1969-1988. Introduction and methods.

Cancer incidence data for Circumpolar Inuit populations were developed and compiled from Greenland, Canada and Alaska from 1969 to 1988 to provide the largest possible base of data for documenting the unusual patterns of cancer previously reported for these populations. Cancer incidence and population data were transferred to the Danish Cancer Registry. Coded information from various ICD-classifications and codes for the basis of diagnosis were transformed to one format, enabling joint analysis. Standard descriptive analysis was carried out with presentation of number of cases, crude incidence rates (CR), age-standardized rates (world) (ASR), cumulative rates to age 64 years, and indirectly standardized ratios (SIR) to the populations of Connecticut (USA), Canada and Denmark. The resulting database can be used to support collaborative international research among the Inuit populations.

Adolescent↗
PubMed1995

Optimization of the Magnetic Bead Antigen Capture Enzyme Immuno Assay for the detection of circulating anodic antigens in mixed Schistosoma infections.

In the present study, simplification and adaptation of the Magnetic Bead Antigen Capture Enzyme Immuno Assay (MBAC-EIA) technique for detection of circulating anodic antigens (CAA) under field conditions was achieved. It was shown that the assay could be performed successfully within the broad temperature range of 18-37 degrees C. The slightly lower sensitivity observed at low temperatures could be adjusted for by prolonging the incubation period. Shaking the plate by hand was as good as automatic mechanical shaking, aspiration of the supernatant before the addition of conjugate was not necessary, and the use of whole blood and serum offered similar assay sensitivity. Furthermore incubation times could be considerably shortened without loss of sensitivity. A major advantage of the MBAC-EIA was that the beads, after elution of bound components, were found to be reusable. The study also showed that the sensitivity of the MBAC-EIA technique in diagnosis of schistosomiasis in a Zimbabwean community endemic for both urinary and intestinal schistosomiasis, was 94%.

Adolescent↗
PubMed1995

Prognostic markers for diet-induced weight loss in obese women.

OBJECTIVE: To identify prognostic metabolic and hormonal markers for long-term weight loss outcome in obese women. DESIGN: Dietary intervention consisting of 36 weeks treatment by a 4.2 MJ/d low-fat high carbohydrate diet, and follow-up 2 1/2 years after termination of treatment. SETTING: Outpatient clinic in Copenhagen. SUBJECTS: Forty consecutive female obese patients aged 15 to 62 years. MAIN OUTCOME MEASURE: Weight loss. RESULTS: The maximum weight loss (mean 16.2 kg, 95% CI 14.2-18.2) was positively associated to pre-treatment 24-h energy expenditure (P < 0.01), fat oxidation (%) (P < 0.02), plasma dihydrotestosterone (DHT) (P < 0.01), and to postprandial noradrenaline concentration (P < 0.04). Together these factors could explain 41% of the variation in maximum weight loss. Only 24-h EE and DHT had predictive power on weight loss after 36 weeks. Weight losses in upper and lower tertiles of DHT concentrations were 17.7 kg (14.1-21.4) and 9.8 kg (6.2-13.3) (P < 0.02). The adjusted relative risk of losing < 10 kg in the upper compared to the lower DHT tertile was 12% (4-32%). At 2 1/2 y follow-up 21 patients had maintained some of the weight loss (54%), while 14 patients had maintained > 5 kg weight loss (36%). High levels of pre-treatment DHT were also associated with better weight loss at 2 1/2 y follow-up. CONCLUSION: The study suggests that in particular DHT, but also 24-h EE, fat oxidation, and plasma noradrenaline, may be prognostic markers for weight loss outcome in obese women.

Adolescent↗
PubMed1994

The first fatal case of Vibrio vulnificus infection in Denmark.

Vibrio vulnificus can cause severe infections in humans and persons with preexisting liver disorders are especially at risk. In this paper we report what is to our knowledge the first fatal case of V. vulnificus infection in Denmark. The patient was a 68-year-old man with a history of chronic lymphatic leukemia and hepatic cirrhosis. Physicians should be aware of the clinical manifestations of this disease and should be especially attentive to patients at risk of acquiring the infection if there has been possible exposure to V. vulnificus by contact with seawater or contaminated material such as eels.

Aged↗
PubMed1993

[Distal femoral fractures treated by external fixation with Orthofix].

In the period from November 1987 to March 1990 17 supracondylar femoral fractures were treated a.m. Orthofix at the orthopaedic departments in Roskilde and Køge, Denmark. The fractures were classified according to Müller et al. There were 13 in group 2A and four in group 3A. In 16 cases the fractures occurred after minimal trauma. Time of operation was 55 minutes (30-150). The patients were fully mobilized after 16 days. The dynamizising procedure took place after six weeks, and the fixator was removed when the fracture was healed after 11 weeks. According to Neer's scoring system the results were good or excellent in 12 cases, and fair on one case. In all patients we found solid bony union. In seven cases we found pin infection. It was not necessary to operate because of the infection in any of these cases. Four cases were complicated with dislocation of the fracture because of bad locking at the ball joint of the fixator. We find this method easy to use in contrast to traditional osteosynthesis. The patients are quickly mobilized. It is easy to correct the fracture and the method gives solid bony healing.

External Fixators↗