Biomedical subjects

D Heitmann

Publications and source records attributed to D Heitmann.

At least 19 recordsLinked to original sources

PubMed2006

Optical modes in semiconductor microtube ring resonators.

We demonstrate optical modes in InGaAs/GaAs microtubes acting as optical ring resonators. Self-supporting microtubes were fabricated by optical lithography and wet-etching processes utilizing the self-rolling mechanism of strained bilayers. The optical modes were probed by the photoluminescence of InAs quantum dots embedded in the tube's wall. In this novel microtube ring resonator we find a spectrum of sharp modes. They are in very good agreement with the theoretical results for a closed thin dielectric waveguide.

Journal Article↗

PubMed2004

Quantized dispersion of two-dimensional magnetoplasmons detected by photoconductivity spectroscopy.

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.

Journal Article↗

PubMed2003

Spectroscopy of few-electron collective excitations in charge-tunable artificial atoms.

We report the investigation of electronic excitations in InGaAs self-assembled quantum dots using resonant inelastic light scattering. The dots can be charged via a gate by N=1, em leader,6 electrons. We observe excitations, which are identified as transitions of electrons, predominantly from the s to the p shell (s-p transitions) of the quasiatoms. We find that the s-p transition energy decreases and the observed band broadens, when the p shell is filled with 1 to 4 electrons. By a theoretical model, which takes into account the full Coulomb interaction in the few-electron artificial atom, we can confirm the experimental results to be an effect of the Coulomb interaction in the quantum dot.

Journal Article↗

PubMed2003

Optical probing of a fractionally charged quasihole in an incompressible liquid.

In photoluminescence spectroscopy of a low-mobility two-dimensional electron gas subjected to a quantizing magnetic field, we observe an anomaly around nu=1 / 3 at a very low temperature (0.1 K) and an intermediate electron density (0.9 x 10(11) cm(-2)). The anomaly is explained as due to perturbation of the incompressible liquid at the Laughlin state due to close proximity of a localized charged exciton which creates a fractionally charged quasihole in the liquid. The anomaly of approximately 2 meV can be destroyed by applying a small thermal energy of approximately 0.2 meV that is enough to close the quasihole energy gap.

Journal Article↗

PubMed2003

Relation between peri-operative antithrombin activity and deep vein thrombosis after elective hip replacement surgery.

BACKGROUND: The purpose of the study was to evaluate whether the postoperative depletion or the preoperative antithrombin (AT) activity is related to the occurrence of deep vein thrombosis (DVT) in patients receiving low-molecular-weight heparin for DVT prevention after elective hip replacement surgery. PATIENTS AND METHODS: In 93 patients AT-activity and standard laboratory parameter were determined on the preoperative day and daily for one week after operation. Furthermore, a color-coded compression sonography was performed before and 8-10 days after surgery. The amount of blood loss and blood transfusions was evaluated. Patients were divided into two groups in respect to the occurrence of a postoperative DVT. RESULTS: The overall incidence of DVT was 8.6% (n = 8). Patients with DVT had a significantly lower preoperative AT-activity (80.6 +/- 3.31%) compared to those without DVT (98.1 +/- 1.12%, p < 0.001), however, without being predictive for DVT (positive predictive value 0.71). There was no association between postoperative fall of AT, the lowest postoperative AT activity, blood loss or blood substitution and DVT. CONCLUSIONS: It has to be expected that a small fraction of patients for elective hip surgery present with AT-activity levels possibly being insufficient for a therapeutic effect of low-molecular-weight heparin even preoperatively. Those patients are subject to a significant higher risk of DVT postoperatively.

Adult↗

PubMed2001

[Recurrent luxations after arthroscopic refixation of the labrum using suture anchors in traumatic ventral shoulder luxation].

OBJECTIVE: Recurrence rates after arthroscopic labral reconstruction for anterior shoulder instability are still higher than after open procedures. Therefore, proper selection of patients becomes increasingly important. The aim of this study was to investigate factors influencing recurrence rates after arthroscopic labral repair with suture anchors. PATIENTS AND METHODS: We examined 53 patients (43 male, 10 female) with traumatic anterior shoulder dislocations, who were treated with arthroscopic labral repair using Fastak-Suture anchors between 1995 and 1996. The average follow-up time was 18 (12-30) months. The mean age of the patients at the time of operation was 27 (15-44) years. RESULTS: Postoperatively, 11 patients (20.7%) reported on redislocations. Recurrence rates increased significantly in patients with more than 4 preoperative dislocations and in patients with bony Bankart lesions. In patients without redislocations, the mean Rowe score improved from 65.9 (SD +/- 12.3) preoperatively to 88.6 (SD +/- 12.5) at follow-up. Thus, there were 24 excellent, 9 good and 6 fair results, while in 3 patients with persisting signs of shoulder instability results had to be estimated as poor. Deficits in the range of motion of more than 15 degrees were seen in 7 patients with predominant affection of the external rotation. CONCLUSION: Frequent preoperative dislocations and bony Bankart lesions contribute substantially to high recurrence rates after arthroscopic labral repair. Therefore, in these cases open procedures should be preferred.

Adolescent↗

PubMed2000

Application of a purge and trap TDS-GC/MS procedure for the determination of emissions from flame retarded polymers.

Emissions of volatile organic compounds (VOCs) from different thermoplastic polymers used in electrotechnical applications were investigated using a purge and trap procedure that involved adsorption on Tenax GR. Results were compared to those for an operating TV set monitored in a test chamber. The analyses were in both cases carried out using thermodesorption gas chromatography with mass spectrometric detection (TDS-GC/MS). Substances identified were monomers, volatile additives, or related compounds. Special attention was given to the detection of halogenated compounds. Their origin was studied using reference samples and synthetic standards.

Air Pollutants↗

PubMed1999

Isolation and structural characterization of glycosphingolipids of in vitro propagated human umbilical vein endothelial cells.

To investigate in detail the expression of glycosphingolipids (GSLs) on endothelial cells, 4.85 x 10(9) human umbilical vein endothelial cells (HUVECs) were cultivated in a 2 l bioreactor using microcarriers as a support for anchorage dependent growing cells. Neutral GSLs and gangliosides were isolated and their structures were determined by TLC immunostaining, fast atom bombardment-mass spectrometry (FAB-MS) of the native GSLs, and gas chromatography-electron impact mass spectrometry (GC-EIMS) of partially methylated alditol acetates. GbOse4Cer, GbOse3Cer, and LacCer, all carrying mainly C24- and C16-fatty acid beside C18-sphingosine, were detected as the major neutral GSLs (36%, 23%, and 15% of the total orcinol stain, respectively); GlcCer, nLcOse4Cer, and nLcOse6Cer were expressed to substantial minor amounts (9%, 12%, and 5% of the total orcinol stain, respectively). TLC immunostaining revealed the presence of lipid bound Lewisx antigen, whereas the isomeric Lewisa structure was detectable only in very low quantities. GM3(Neu5Ac) with C18-sphingosine was the major ganglioside constituting about 90% of the whole ganglioside fraction. The fatty acid composition was determined by GC-MS of fatty acid methyl esters, indicating the predominance of C24- and C16-substituted GM3(Neu5Ac), followed by C18- and C22-substituted species. Terminally alpha2-3 sialylated neolacto-series ganglioside IV3Neu5Ac-nLcOse4Cer was the second most abundant ganglioside in HUVECs (8% of the total resorcinol stain), and IV6Neu5Ac-nLcOse4Cer and VI3Neu5Ac-nLcOse6Cer (together less than 2% of total resorcinol stain) were found in minor quantities. Lipid bound sialyl Lewisx antigen with poly-N-acetyllactosaminyl chains, and traces of gangliotetraose-type gangliosides GM1 and GD1a were identified by TLC immunostaining. The expression of dominant neutral GSLs LacCer, GbOse3Cer, and GbOse4Cer, and of ganglioside GM3(Neu5Ac) was assayed by indirect immunofluorescence microscopy of cell layers grown in chamber slides, each showing different plasma membrane and subcellular distribution patterns. The complete structural characterization of GSLs from HUVECs contributes to our understanding about their functional role, not only of the carbohydrate but also of the lipid moiety, as receptors for bacterial toxins, as cell surface antigens of cellular interaction and as receptors for blood components and macromolecules of the extracellular matrix.

Bioreactors↗

PubMed1998

Large scale purification of gangliosides GM3(Neu5Ac) and GM3(Neu5Gc) by trimethylaminoethyl-Fractogel high-performance liquid chromatography.

A preparative anion-exchange high-performance liquid chromatographic method for the separation of the closely allied monosialogangliosides GM3(Neu5Ac) and GM3(Neu5Gc) has been developed. Hybridoma cells, readily available material derived from industrial monoclonal antibody production, were used as ganglioside source and led to fractions with pure GM3(Neu5Ac) and GM3(Neu5Gc) in high milligram quantities. The crude ganglioside extract was loaded onto columns filled with the strong anion-exchanger trimethylaminoethyl (TMAE)-Fractogel. Gangliosides were eluted from the stationary phase with a gradient system of ammonium acetate in methanol. The scaled-up approach ranged over more than one order of magnitude from 20 to 500 mg batches of GM3 gangliosides. Thus, the high-resolution power of the strong anion-exchanger TMAE-Fractogel allowed the preparative isolation by one-step column chromatography of two GM3 specimens which only differ in one hydroxyl group at position 5 of the neuraminic acid (N-acetyl-versus N-glycolylneuraminic acid).

Animals↗

PubMed1998

[Changes in proprioceptive capacities of the shoulder joint in ventral shoulder instability. A comparative study before and after arthroscopic labrum refixation].

Measurements of movement sense determined by threshold levels for the perception of motion of the shoulder were performed in 10 patients with unilateral posttraumatic shoulder instabilities, in 30 patients who underwent arthroscopic labrum repair for recurrent anterior shoulder instability, and in 15 age-related controls. In patients with anterior shoulder instabilities threshold levels for the perception of motion were higher. In addition, movement sense measurements revealed a marked, but time dependent improve of proprioceptive abilities in patients who underwent arthroscopic labrum repair. While in the shoulders of patients with an postoperative period shorter than 18 months elevated threshold levels for the perception of motion still could be observed, after a postoperative period of 18 moths or more movement sense was not different from normal, uninjured shoulders. In conclusion, our study gives evidence for a proprioceptive deficit with anterior shoulder instability which improves significantly after arthroscopic labrum repair. The restitution of proprioceptive abilities, however, seems to be a time dependent process.

Adult↗

PubMed1996