PubMed Health⌕ Search

Biomedical subjects

M Meixner

Publications and source records attributed to M Meixner.

At least 19 recordsLinked to original sources
PubMed2001

Self-assembled quantum dots: crossover from kinetically controlled to thermodynamically limited growth.

By means of kinetic Monte Carlo simulations of the self-organized growth of quantum dots in strained semiconductor systems we resolve the seemingly contradictory features of kinetic versus thermodynamic behavior, e.g., with respect to the temperature dependence of the average dot size and their dispersion. We show that the size distribution immediately after deposition is kinetically controlled, with smaller islands for lower temperatures and larger islands for higher temperatures. For longer simulation times the kinetics leads to equilibration, and a crossover effect between the size distributions occurs, which is in good agreement with the predictions of thermodynamics.

Journal Article↗
PubMed2001

Cutaneous elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

BACKGROUND: After exposure, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is excreted via the faeces, breast milk and epidermal lipids. OBJECTIVES: To determine to what extent TCDD is eliminated via the skin and to evaluate whethe cutaneous elimination can be accelerated by the application of petrolatum. METHODS: In two patients severely intoxicated with TCDD, material obtained from the skin surface and, in one patient, cerumen and the content of epithelial cysts, was analysed for TCDD. RESULTS: The TCDD concentration in the initial blood sample taken was 144 000 pg g(-1) blood fa in patient 1, and 26 000 pg g(-1) blood fat in patient 2. Six months later, when the skin tests were performed, the blood TCDD levels had decreased to 80 900 and 16 100 pg g(-1) blood fat, respectively. In the two samples of pooled cyst contents from patient 1, TCDD levels of 34 400 an 18 600 pg g(-1) fat were found. A cerumen sample contained TCDD at 20 500 pg g(-1) fat. In the material collected from the skin surface we observed a linear increase of the amount of TCD measured per test field with time, indicating a continuous elimination of TCDD via the skin. Th daily amount of TCDD eliminated via the skin was 1.51 pg cm(-2) in patient 1 and 0.57 pg cm(-2) in patient 2. Application of petrolatum led to a twofold increase in the amount of TCDD measured in patient 1, but had no significant effect in patient 2. CONCLUSIONS: In our patients, elimination of TCDD via the skin, most probably through desquamating scales, represented 1-2% of the overall daily TCDD elimination rate, with regard to the body surface and when calculated on the basis of the half-life of TCDD at the time of the skin test. If a more typical overall elimination half-life of 7 years is used as the basis for the calculatio the skin would account for 9% (patient 1) and 15% (patient 2) of the overall elimination. Although we observed an increase in TCDD in material derived from the skin surface of up to 100% after application of petrolatum in patient 1, such an approach appears not to be a feasible means to increase elimination. Owing to the small amount of TCDD measured in skin-surface material, as well as in the cyst contents and cerumen obtained from one patient, contamination of the environment and other persons appears highly unlikely.

Acne Vulgaris↗
PubMed2000

Karhunen-Loeve local characterization of spatiotemporal chaos in a reaction-diffusion system

By computing the Karhunen-Loeve decomposition (KLD) correlation length xi(KLD) of a reaction-diffusion system in the extensive chaos regime, we show that it is a sensitive measure of spatial dynamical inhomogeneities. It reveals substantial spatial nonuniformity of the dynamics at the boundaries and can also detect slow spatial variations in system parameters. The intensive length xi(KLD) can be easily computed from small local subsystems and is found to have a similar parametric dependence as the two-point correlation length computed over the full system size.

Journal Article↗
PubMed1999

Olestra increases faecal excretion of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Two patients with chloracne had concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) of 144,000 and 26,000 pg/g blood lipids. Olestra, a non-digestible, lipophilic dietary fat substitute accelerated the patients' intestinal excretion of TCDD by eight to ten fold. This is sufficient to reduce the normally observed elimination half life of TCDD from about 7 years to 1-2 years.

Acne Vulgaris↗
PubMed1999

Green fluorescent protein as a marker to investigate targeting of organellar RNA polymerases of higher plants in vivo.

The recent identification of phage-type RNA polymerases encoded in the nuclear genome of higher plants has provided circumstantial evidence for functioning of these polymerases in the transcription of the mitochondrial and plastid genomes, as demonstrated by sequence analysis and in vitro import experiments. To determine the subcellular localization of the phage-type organellar RNA polymerases in plants, the putative transit peptides of the RNA polymerases RpoT;1 and RpoT;3 from Arabidopsis thaliana and RpoT from Chenopodium album were fused to the coding sequence of a green fluorescent protein (GFP). The constructs were used to stably transform A. thaliana. Transgenic plants were examined for green fluorescence with epifluorescence and confocal laser scanning microscopy. Plants expressing the GFP fusions under control of the CaMV35S promoter exhibited a distinct subcellular localization of the GFP fluorescence for each of the fusion constructs. In plants expressing GFP fusions with the putative transit peptides of ARAth;RpoT;1 and CHEal;RpoT, fluorescence was found exclusively in mitochondria, both in root and leaf cells. In contrast, GFP fluorescence in plants expressing the ARAth;RpoT;3-GFP construct accumulated in chloroplasts of leaf cells and nongreen plastids (leucoplasts) of root cells. By demonstrating targeting in plants, the data add substantial evidence for the phage-type RNA polymerases from C. album and A. thaliana to function in the transcriptional machinery of mitochondria and plastids.

Arabidopsis↗
PubMed1998

Analysis of cytokine patterns produced by individual CD4+ lymph node cells during experimental murine leishmaniasis in resistant and susceptible mice.

The concept of subdividing CD4+ T cells into Th0, Th1 and Th2 cells is based on the cytokine pattern produced by long-term in vitro cultured T cell lines. However, there exists uncertainty whether this classification can also be applied to CD4+ T cells in vivo. Herein it was investigated whether and at which frequency Th0, Th1 and Th2 cells are induced in vivo during an infection of mice with Leishmania major. Cytokine co-production in single IFN-gamma+ or IL-4+ CD4+ T cells as well as the frequency of such cells were assessed in the lymph nodes (LN) of infected mice. For this purpose, T cells derived from the draining LN were activated by phorbol myristate acetate (PMA)/ionomycin, and the intracellular cytokines IL-2, IL-4, IL-5, IL-10 and IFN-gamma were analyzed by immunofluorescence. One week after infection, a strong, but comparable increase of IFN-gamma+ CD4+ and IL-4+ CD4+ cells (up to 7% of all CD4+ cells) in the LN was observed in resistant C57BL/6 mice and susceptible BALB/c mice. IFN-gamma and IL-4 were not co-produced by single cells ('Th0 cells'). At later stages of the infection, the number of IL-4+ CD4+ cells decreased in C57BL/6, but not in BALB/c mice. All IL-4+ CD4+ cells showed an unexpected phenotype, because at least half of these cells co-produced IL-2, and the majority of the IL-4+ CD4+ did not co-produce the Th2 cytokines IL-5 and IL-10. Similar cytokine profiles were obtained when the CD4+ T cells were stimulated by Leishmania major-antigen instead of PMA/ionomycin. This study demonstrates that 'classical' Th1 cells (IFN-gamma+IL-2+), but no 'classical' Th2 cells (IL-4+IL-5+IL-10+) and no Th0 cells (IFN-gamma+IL-4+) are generated during L. major infection of mice in vivo.

Animals↗
PubMed1993

[A method for determining the denominator in general practice--results of a pilot study].

In countries with fee for service billing and direct access to specialist care the general practitioner does not know key figures of the population he serves. As the role of general practice in health-service-research, quality assurance activities and the construction of sentinel-networks is becoming more important, valid methods to determine the denominator are needed. Results from five practices suggest that yearly contact groups should be used as a common denominator for general practice in our health care system. For certain groups of patients (e. g. the elderly > 60 yrs.) even quarterly contact groups can give sufficient information to forecast the yearly contact group.

Adolescent↗
PubMed1987

[A hierarchy of findings within the scope of cerebrovascular diagnosis today].

Table 5 gives an overview as to the timing and indication for diagnostic methods and procedures in cerebro-vascular diseases. Anamnesis and clinical aspects have still leading position. After that, computer-tomography stands first in the diagnostic line, followed by angiography, indicated in the acute phase only in progressive stroke. More often it is used during rehabilitation period for indication towards extra-intracranial anastomosis. Sonography gives informations specially in the extracranial stenoses by duplex sonography. The EEG is still necessary in the early stage and for follow-ups. Cerebro spinal fluid analysis, intern medicine (mainly cardiology) examinations, give extra information and should not be skipped. Psychological exams and intracranial bloodflow-studies are used during rehabilitation. Digital angiography, with the possibility of postprocessing, is in comparison to conventional angiography, less invasive. Nuclear-magnetic-resonance with its fast development is taking now place in the clinical field. Cerebro-vascular patients should be treated in specialized centers where beside the equipment, an experienced team is available, which has required its knowledge on a high number of cases and where the cooperation between the different fields of conservative (intern and neurology) radiology and surgery is guaranteed. This paper however has tried to show the up-to-date-guidelines to the other medical specialties that handle cerebrovascular patients.

Brain Ischemia↗
PubMed1978

[Bone scans in the diagnosis of renal osteopathy].

Biochemical tests (serum calcium, inorganic phosphate and alkaline phosphatase), as well as clinical, radiological, scanning and histological investigations were undertaken in 24 patients in chronic renal failure. The frequency with which the diagnosis of renal osteopathy could be made depended in the method of investigation, the biochemical findings proving to be completely unreliable. There were positive radiological signs in ten patients and clinical signs in 12, predominantly in the progressive stages of osteopathy. A positive scan was obtained in 23 patients, typical histological bone changes in an equal number. Since it correlates so well with the histological findings, bone scan is suitable particularly in the early diagnosis of osteopathy. Since this test is easily performed and hardly stresses the patient, it should routinely be the initial one for the diagnosis of renal osteopathy.

Adult↗
PubMed1978

[Bone scan in the diagnosis of renal osteopathy (author's transl)].

Biochemical tests (serum calcium, inorganic phosphate and alkaline phosphatase), as well as clinical, radiological, scanning and histological investigations were undertaken in 24 patients in chronic renal failure. The frequency with which the diagnosis of renal osteopathy could be made depended in the method of investigation, the biochemical findings proving to be completely unreliable. There were positive radiological signs in ten patients and clinical signs in 12, predominantly in the progressive stages of osteopathy. A positive scan was obtained in 23 patients, typical histological bone changes in an equal number. Since it correlates so well with the histological findings, bone scan is suitable particularly in the early diagnosis of osteopathy. Since this test is easily performed and hardly stresses the patient, it should routinely be the initial one for the diagnosis of renal osteopathy.

Adolescent↗
PubMed1977

Liver and spleen scanning as a useful diagnostic test in the management of liver trauma in young patients.

Liver and spleen scanning is a safe, fast and noninvasive diagnostic procedure. With the advent of mobile Gamma Cameras it can be ideally performed in a casualty department. The number of patients with traumatic blunt injuries to the abdomen is increasing and in correlation with the increased speed and concentration of traffic. In eleven patients with ages ranging between 4 and 23, and under observation for violent trauma to the abdomen, liver and spleen scanning was performed either as an emergency procedure or as a follow-up study. Very useful information was obtained regarding the integrety of these organs, before and or after emergency surgical treatment.

Abdominal Injuries↗
PubMed1976

Specific diagnosis of brain disease with double isotope brain scanning.

25 patients with known cerebral disease (either CVA's or primary or secondary tumours) diagnosed by clinical and angiographic criteria were submitted to a double isotope imaging technique using 99mTcO4- and 99mTc-EHDP. The different biological behaviour of these radiopharmaceuticals has provided specific and differential diagnosis between vascular and neoplastic disease of the brain. 99mTc-EHDP is shown to be the tracer of choice for the imaging of CVA's and 99mTcO4- is confirmed as the tracer of choice for the imaging of primary or secondary tumours in the brain.

Adult↗