Search Results - (Author, Cooperation:S. Geier)

2015-03-07

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A novel method yielding simultaneous information about location and orientation of the crystallites in a polycrystalline specimen has been developed and succesfully applied to the investigation of thin diamond films deposited on silicon. The experiment uses the parallel beam from a synchrotron radiation source and a microchannel plate as collimator in front of an image plate detector. Exposure times of only a few minutes could be realized. The spatial resolution was 0.375 mm but can easily be improved. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Oriented diamond films have been grown on Si(001) and Si(111) substrates by microwave plasma chemical vapor deposition. X-ray diffractometry has been employed for pole figure measurements which have been evaluated by the component method. This technique can be applied to multiphase materials with overlapping pole figures. It decomposes the texture into components by identifying preferred directions in the pole density distribution. Thereby the textures of both diamond on Si(001) and on Si(111) have been reproduced quantitatively elucidating the heteroepitaxial orientational relationship and the occurrence of twinning. The volume fractions of both epitaxially oriented diamond crystallites and their twins of first order have been determined. It is shown that under the employed nucleation and growth conditions twinning is more pronounced for diamond on Si(111) than on Si(001). Furthermore, the fraction of randomly oriented crystallites in both textures has been determined. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Very thin diamond films (thickness ∼0.1 μm) have been investigated by x-ray diffraction pole figure measurements using synchrotron radiation in order to understand the mechanism of heteroepitaxial diamond nucleation and the first steps of film growth on silicon(001) substrates. The diamond layers consist of an epitaxially aligned component with a crystallographic orientation identical to the substrate. The initial orientational spread of the grains around the perfect epitaxial orientation prior to any modification by a subsequent textured growth step has been determined. In the studied temperature range for the nucleation step the misalignment decreases slightly with increasing temperature. Besides the epitaxial crystallites their corresponding twins of first and second order have been found. The intensity distribution of the pole figures indicates that the process of twinning plays a dominating role in the initial growth stage which shows a tendency to become even more pronounced for higher substrate temperatures. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beam has been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the orientational arrangement of and among individual diamond crystallites in the near-interface region. A comparison with the orientation of the substrate has proved the existence of epitaxially nucleated grains. A high amount of twinned diamond has been deduced from the pole figures and verified by analysis of orientation correlations between neighboring crystallites. Moreover, the grain boundary maps have allowed us to monitor and quantify directly the occurring twin boundaries. © 1994 American Institue of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have developed a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles. The particles are placed in an evanescent field produced by total internal reflection of light from a halogen lamp in a glass prism. The light scattered by individual particles is collected using a conventional microscope and is spectrally analyzed by a nitrogen-cooled charge-coupled-device array coupled to a spectrometer. This technique is employed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles. We also demonstrate the use of this technique for measurements in liquids, which is important for the potential application of particle plasmons in chemical or biological nanosensors. © 2000 American Institute of Physics.

Electronic Resource

0022-2836

Escherichia coli ; NADH : ubiquinone oxidoreductase ; complex I ; gene order ; sequences

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0038-1098

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

1432-1440

HIV-1 ; Endothelins ; Endothelin-1 ; Cytokine ; Retinal microangiopathic syndrome ; Vascular disease

Springer Online Journal Archives 1860-2000

Medicine

Abstract Endothelin-1 is a recently identified cytokine with potent vasoconstrictor activity which is associated with various diseases involving blood vessels. HIV-1 related retinal microangiopathic syndrome is a frequent finding in patients with AIDS or AIDS-related complex, presenting predominantly with retinal cotton-wool spots. We investigated 55 HIV-1 infected patients by ophthalmoscopy and for endothelin-I immunoreactivity in plasma and an additional 76 HIV-1 infected patients only for endothelin-1 levels. For reference values 13 age-matched healthy subjects were studied. In 18 of 55 patients (33%) investigated ophthalmoscopically we found evidence of microangiopathic syndrome. Overall, the mean endothelin-1 immunoreactivity in plasma of HIV-1 infected patients was significantly elevated as compared to controls (4.28 ± 3.62 versus 2.72 ± 0.67 fmol/ml, P 〈 0.0001). HIV-1 infected patients with retinal microangiopathic syndrome had significantly higher plasma levels of endothelin-1 immunoreactivity (4.59 ± 1.38 fmol/ ml) compared to HIV-1 infected patients without microangiopathic syndrome (3.18 ± 1.64 fmol/ml, P = 0.003). Correlation analysis revealed that endothelin-1 immunoreactivity in plasma had no significant association with disease progression, CD4 cell count, β2-mi-croglobulin, neopterin, or age. Endothelin-1 immunoreactivity in plasma was correlated exclusively with retinal microangiopathic syndrome in one or both eyes (r = 0.45, P = 0.0006) and with the number of cotton-wool spots (r = 0.50, P = 0.0001). In conlusion, HIV-1 related retinal microangiopathic syndrome is associated with elevated plasma levels of endothelin-1. By virtue of its potent vasoconstrictor activity endothelin-1 may be involved in the pathogenesis of HIV-1 related vascular disease.

Electronic Resource

1432-0630

PACS: 68.55; 61.10

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Abstract.  Thin SiC films have been deposited on silicon(0 0 1) substrates by fullerene-carbonization. Using synchrotron radiation X-ray diffraction pole figure measurements have been employed in order to study the texture of the layers. It is qualitatively shown that the films contain epitaxially aligned β-SiC crystallites with the same orientation as the underlying substrate and their twins of first and second order. The orientational spread of the epitaxial crystallites in terms of tilt against and rotation around the substrate normal is smaller than 3°. The formation of twins as a growth defect plays a major role which is even more pronounced at a higher substrate temperature. Furthermore, an additional preferred orientation has been identified which can only be explained by a non-cubic SiC phase. The portion of these crystallites in the film can be considerably reduced by an increase of the deposition temperature.

Electronic Resource

1432-0630

68.55 ; 61.10 ; 81.40.Ef

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Abstract The growth of epitaxial C60 thin films on mica(001) by thermal evaporation has been studied in detail by X-ray pole-figure measurements. The influence of the deposition rate, the substrate temperature and the film thickness on the in-plane epitaxial arrangements and the formation of twins has been investigated. It has been demonstrated that the C60 growth is determined by two independent and equivalent C60-crystal grain alignments (type-A and type-B). The nearly six-fold symmetry of the mica(001)-substrate surface offers the three-fold fcc-(111)-oriented C60-crystal grains two equivalent crystal alignments. A high deposition rate of 0.5 Å/s is responsible for the formation of twins at a substrate temperature of 150°C, which diminishes by a higher substrate temperature of 200°C. By a decrease of the deposition rate down to 0.08 Å/s the twins vanish at a film thickness of 200 nm and at the substrate temperature of 150°C. Under the same sublimation conditions, in addition to the type-A and type-B crystal orientations, the growth of the thin C60 films starts with a slight fibre texture which does not appear at a larger film thickness.

Electronic Resource

1432-0630

PACS: 68.55; 61.10; 81.40.Ef

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Abstract. The growth of epitaxial C60 thin films on mica(0 0 1) by thermal evaporation has been studied in detail by X-ray pole-figure measurements. The influence of the deposition rate, the substrate temperature and the film thickness on the in-plane epitaxial arrangements and the formation of twins has been investigated. It has been demonstrated that the C60 growth is determined by two independent and equivalent C60-crystal grain alignments (type-A and type-B). The nearly six-fold symmetry of the mica(0 0 1)-substrate surface offers the three-fold fcc-(1 1 1)-oriented C60-crystal grains two equivalent crystal alignments. A high deposition rate of 0.5 AÅ/s is responsible for the formation of twins at a substrate temperature of 150° C, which diminishes by a higher substrate temperature of 200° C. By a decrease of the deposition rate down to 0.08 AÅ/s the twins vanish at a film thickness of 200 nm and at the substrate temperature of 150° C. Under the same sublimation conditions, in addition to the type-A and type-B crystal orientations, the growth of the thin C60 films starts with a slight fibre texture which does not appear at a larger film thickness.

Electronic Resource

1439-0973

Springer Online Journal Archives 1860-2000

Medicine

Zusammenfassung Neben der Infektionsgefahr durch HIV-haltiges Blut interessiert Ophthalmologen vor allem auch die Möglichkeit einer Infektion über die Tränenflüssigkeit. Wir haben deshalb versucht, HIV-1 aus der Tränenflüssigkeit von 50 HIV-1-infizierten Personen in unterschiedlichem Stadium der Erkrankung zu isolieren und über Reverse Transkriptase (RT) sowie p24-Antigen (p24-AG) im Kulturüberstand nachzuweisen. Parallel hierzu wurde aus dem Kulturüberstand peripherer Blutlymphozyten (PBL) der jeweiligen Personen eine Virusisolierung versucht. Dies gelang in 32 der 50 Fälle. Dagegen konnte in keinem Fall HIV-1 aus den Tränen der entsprechenden Personen isoliert werden. Zusätzlich wurde versucht, bei 10 HIV-1-infizierten Patienten in Tränenflüssigkeit und PBL provirale Sequenzen (gag, pol, env) von HIV-1 mittels der Polymerase-Ketten-Reaktion (PCR) nachzuweisen. Während dies in allen 10 Fällen mit PBL gelang, konnte nur in einem Fall HIV-DNA über gag- und pol-Amplifikate in der Tränenflüssigkeit nachgewiesen werden. Diese Ergebnisse sprechen für einen niedrigen Gehalt der Tränenflüssigkeit an gewebeinfektiösen Einheiten von HIV-1 im Vergleich mit dem Blut HIV-1-infizierter Personen. Damit scheint eine Infektion über den Kontakt mit Tränenflüssigkeit HIV-1-Infizierter weiter unwahrscheinlich.

Summary Beside the risk of infection via HIV-1-contaminated blood, ophthalmologists are especially interested in the possibility of HIV-1 infection via tears. Therefore we tried to isolate HIV-1 from tears of 50 HIV-1-infected persons in different stages of disease by reverse transcriptase (RT) and by p24-antigen (p24-AG) in the cultures. Simultaneously we tried to isolate HIV-1 in the supernatant from peripheral blood lymphocytes (PBL), which was successful in 32 of the 50 examined specimens. HIV-1 could not be isolated from the tears of these persons. In addition, polymerasechain-reaction (PCR) was performed to detect proviral sequences (gag, pol, env) of HIV-1 in tears and blood of ten HIV-1-infected patients. While in all the examined patients gag, pol and env could be detected in the blood samples, only one tear sample was found positive for gag and pol DNA fragments. These results indicate that tears of HIV-1-positives contain extremely low quantities of tissue culture infectious doses (TCID) of HIV-1 in contrast to PBL. HIV-1 infection via tears therefore appears to be unlikely.

Electronic Resource