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Biomedical subjects

W Widdra

Publications and source records attributed to W Widdra.

11 recordsLinked to original sources
PubMed2006

Two bonding configurations of acetylene on Si(001)-(2 x 1): a combined high-resolution electron energy loss spectroscopy and density functional theory study.

Two coexisting adsorption states of molecularly adsorbed acetylene on the Si(001)-(2 x 1) surface have been identified by a combined study based on the high-resolution electron energy loss spectroscopy and density functional computations. Seven possible adsorbate-substrate structures are considered theoretically including their full vibrational analysis. Based on a significantly enhanced experimental resolution, the assignment of 15 C2H2- and C2D2-derived vibrational modes identifies a dominant di-sigma bonded molecule adsorbed on top of a single Si-Si dimer. Additionally there is clear evidence for a second minority species which is di-sigma bonded between two Si-Si dimers within the same dimer row (end-bridge geometry). The possible symmetries of the adsorbate complexes are discussed based on the specular and off-specular vibrational measurements. They suggest lower than ideal C(2v) and C(s) symmetries for on-top and end-bridge species, respectively. At low coverages the symmetry reductions might be lifted.

Journal Article↗
PubMed2006

Interaction of SO3 with c-ZrO2(111) films on Pt(111).

Single-crystalline sulfated c-ZrO2(111) films of the cubic (c) type have been prepared by reactive deposition of Zr onto Pt(111) in an O2 atmosphere and subsequent exposition to a SO3 atmosphere. The morphology, atomic structure, and composition have been examined by scanning tunneling microscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, and density functional theory (DFT) calculations. The clean c-ZrO2(111) films display a (2x2) surface structure. During SO3 exposure at room temperature, a clear (radical3xradical3)R30 degrees structure develops. At about 700 K, the SO3-induced (radical3xradical3)R30 degrees structure disappears and the bright (2x2) LEED pattern of the clean ZrO2 films reappears. The energies of plausible c-ZrO2(111)/SO3 structures have been examined by DFT. The (radical3xradical3)R30 degrees structure found in the experiments turned out to be the most stable one for temperatures below 700 K. At temperatures around 700 K, a disordered low coverage structure may exist, which can not be observed by conventional LEED. A comparison of cubic zirconia surfaces with the alternative tetragonal system yields similar results for the SO3 adsorption in the DFT calculations and shows that c-ZrO2 surfaces are good models for the industrial used tetragonal ZrO2 supports.

Journal Article↗
PubMed2006

Pressure-dependent Ni-O phase transitions and Ni oxide formation on Pt(111): an in situ STM study at elevated temperatures.

Growth, atomic structure and O2 partial pressure dependent phase transitions of Ni-O structures and thin NiO films on Pt(111) have been studied using scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). In situ STM experiments were performed during film growth by reactive metal deposition at elevated temperatures (400-550 K) and variable O2 pressure. Depending on the substrate temperature, one-dimensional network-like Ni-O structures and islands with (7x1) and (4x2) reconstructions are formed during the initial stages of growth. These structures transform reversibly to a (2x2) reconstruction in a narrow O2 pressure range of 1.5-2x10(-6) mbar and can be monitored by in situ STM. Upon reduction of the O2 pressure to <10(-10) mbar pseudomorphic Ni monolayers are obtained. The defect-free ordering of Ni atoms on Pt(111) in a single stacking domain indicates an O-surfactant induced growth mode. The structural properties of the O2 pressure-dependent Ni-O phases are discussed in a simple model assuming NiO(001)-like atomic arrangements in the adsorbate overlayer. At higher coverage stable (111)-oriented NiO islands grow in a three-dimensional mode.

Journal Article↗
PubMed2006

Charging mechanisms of trapped element-selectively excited nanoparticles exposed to soft x rays.

Charging mechanisms of trapped, element-selectively excited free SiO2 nanoparticles by soft x rays are reported. The absolute charge state of the particles is measured and the electron emission probability is derived. Changes in electron emission processes as a function of photon energy and particle charge are obtained from the charging current. This allows us to distinguish contributions from primary photoelectrons, Auger electrons, and secondary electrons. Processes leading to no change in charge state after absorption of x-ray photons are identified. O 1s-excited SiO2 particles of low charge state indicate that the charging current follows the inner-shell absorption. In contrast, highly charged SiO2 nanoparticles are efficiently charged by resonant Auger processes, whereas direct photoemission and normal Auger processes do not contribute to changes in particle charge. These results are discussed in terms of an electrostatic model.

Journal Article↗
PubMed2005

Photoelectron spectroscopy on thin films of extended zinc porphyrazines.

Photoemission measurements were performed on a series of stepwise benzoannelated zinc porphyrazine molecules in thin films. The electronic structure of tert-butyl-substituted zinc tetraazaporphyrin, phthalocyanine, and naphthalocyanine is investigated using mainly EUV synchrotron radiation. A detailed analysis of the zinc satellites in the spectra of the valence region is performed in an attempt to infer the effect of ligand size extension on the metal-ligand interactions. No differences in the character of the bond between zinc and ligand were detected as a function of ligand size. The results are compared with those for the respective metal-free and copper-containing molecules.

Organometallic Compounds↗
PubMed2001

Two-Phonon States and Overtone Delocalization in One-Dimensional Systems of Oscillators: Vibrational Spectroscopy of a NO Adsorbate Row Structure.

We report on a strong overtone delocalization in one-dimensional systems due to interaction with the two-phonon state. Whereas this interaction leads to small continuous shifts in comparable two-dimensional systems we find a discontinuous shift with bond anharmonicity in one dimension. As a consequence no overtone features can be observed in the spectral function. Experimentally, the phonon dispersion for a quasi-one-dimensional adsorbate system, molecular NO rows in the well-ordered (NO+O)-(2x1) phase on Ru(001), has been mapped out using electron energy loss spectroscopy. The internal NO mode shows a strong band dispersion of 110 cm(-1) along the molecular row. In the region of its overtone the spectra show a peak structure and a nonvanishing background which is interpreted as an overtone-modified two-phonon state.

Journal Article↗
PubMed1990

Efficacy and safety of intranasal buserelin acetate in the treatment of endometriosis: a review of six clinical trials and comparison with danazol.

The efficacy and safety of buserelin acetate in the treatment of endometriosis was studied in 4 open non-comparative trials and 2 open randomized comparative trials with danazol. 444 women were enrolled in the buserelin group and 89 in the danazol group. Treatment was for 6-10 months using 900-1200/micrograms intranasal buserelin/day and 400-800/micrograms oral danazol/day; patients were followed up for 6-8 months. Endometriotic lesions improved or disappeared in most women; pain (dysmenorrhoea, dyspareunia and pelvic pain) subsided rapidly. Most women had no, or alleviated, symptoms throughout follow-up, although ovarian function resumed promptly. Nearly a quarter of infertile women with a desire for children became pregnant. No significant differences between treatments emerged. Buserelin treatment was characterized by menopausal-like symptoms in most women, as well as by headache and nausea. Danazol treatment, which also gave rise to these effects, was accompanied by weight gain, myalgia and acne in a considerable proportion of women, as well as other anabolic and androgenic side effects. Buserelin would thus appear to be a safe and effective alternative to the standard therapy, danazol, in the treatment of endometriosis.

Administration, Intranasal↗
PubMed1990

[Biochemical aspects of the evaluation of fixed drug combinations].

Various disciplines have to contribute to the general problem of the evaluation of fixed dose combination drugs, as for instance (clinical) pharmacology, biometry, scientific drug regulations and public health officials. The EC guideline 75/318/EWG and its eludications as well as the German "Arzneimittelprüfrichtlinien" of Dec. 14, 1989 (as referred to in the "Arzneimittelgesetz" of 1986) required that such issues concerning fixed dosage combination drugs must be considered and taken into account. In this framework it is the responsibility of biometry to both to guarantee the use of a valid study design to assure interpretation of the results and to quantify the reliability of pharmacological and clinical considerations. The following paper is concerned with biometrical aspects of the combination drug problem. Basic considerations from a clinical or a pharmacological point of view with respect to the question of whether fixed combination drugs are reasonable or not are not discussed. To support the use of combinations of drugs, a central argument is the improvement of the benefit risk relation compared with that of an adequate monotherapy. Beyond this the fixed combination drugs require additional arguments regarding the enhencement of the safety or the simplicity of the therapy fixing the ratio. It follows that fixed combination drugs have to be supported twice, first with respect to the combination itself, and second with respect to the fixed mixing ratio of its components. The biometrical aspects of the assessment of the gains from (fixed) drug combinations are related to the kind of benefit/risk improvement that is expected. In the first section we discuss some possible types of benefit and risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗