ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Digitale Medien

New features of the Mott-Hubbard insulator gap of parent HTS compounds found by resonance Raman scattering and UV-excited ordinary Raman scattering (1994)

Klein, M. V. ; Liu, Ran ; Salamon, D. ; [weitere]

Springer

Journal of superconductivity 7 (1994), S. 429-433

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1572-9605

Schlagwort(e): Raman scattering ; magnon ; exciton ; charge-transfer excitation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract Optical absorption at the insulating gap in the parent phase of cuprate superconductors shows a broad exciton-like peak near 1.7 eV, followed by a gradual decrease in absorption persisting 1 eV above the gap. By using ultraviolet laser lines to excite Raman spectra, we have found a Raman peak 0.2 eV below the first absorption peak in insulating cuprates. The Raman peak is much narrower than the absorption peak and hasA 2g symmetry. We assign it to an exciton consisting of a hole transition from Cu $$d_{x^2 - y^2 } $$ to a linear combination of Cud xy and nearest neighbor Op π orbitals. We have also studied the resonance Raman profile for two-magnon Raman scattering in the same samples. We find a sharp resonance feature at about 2.7 eV, and little Raman intensity for photon energies at the 1.7 eV absorption peak. The state created at the peak must therefore be an inappropriate intermediate state for the double spin-flip Raman process.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00724583

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

2

Digitale Medien

Segmental orientation studies of polyether polyurethane block copolymers with different hard segment lengths and distributions (1985)

Lin, S. B. ; Hwang, K. S. ; Tsay, S. Y. ; [weitere]

Springer

Colloid & polymer science 263 (1985), S. 128-140

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1435-1536

Schlagwort(e): Polyurethane ; segmental ; orientation ; infrared ; dichroism

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau

Notizen: Abstract The orientation behavior of two series of segmented polyether polyurethanes containing different hard segment length distributions has been studied as a function of the average hard segment length which was varied from one to five methylene bis (p-phenyl isocyanate) (MDI) units. The orientation behavior of the soft segments, isolated hard segments, and of hard segments aggregated in hard domains was determined from the dichroic behavior of representative infrared bands. As the hard segment length increases, a transition in orientation behavior is observed which corresponds to a change in sample morphology. The effects of annealing and hard segment length distribution were also studied and were shown to affect the orientation response through their influence on sample morphology. Orientation hysteresis studies were performed to probe the mechanism of the transverse orientation and orientation inversion which occurred in polyurethanes with the longer, more crystallizable hard segment lengths.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01412787

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

3

Digitale Medien

EXAFS and XANES studies of Zn2+ and Rb+ neutralized perfluorinated ionomers (1984)

Pan, H. K. ; Knapp, G. S. ; Cooper, S. L.

Springer

Colloid & polymer science 262 (1984), S. 734-746

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1435-1536

Schlagwort(e): Microstructure ; nafion ; ionomer ; EXAFS ; XANES

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau

Notizen: Abstract Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) experiments have been carried out to probe the Zn2+ and Rb+ environment in perfluorinated ionomers. The cation environment has been determined for these ionomers in their dry, hydrated and n-amyl alcohol swollen state. It was found that a well ordered, crystalline-like nearest-neighbor oxygen shell predominates in the zinc neutralized perfluorinated ionomers. Unlike the zinc ionomers, the Rb+ neutralized ionomers show no discernible peaks in the radial structure function indicating that the rubidium environment is highly disordered. Coordination of the hydroxyl groups of namyl alcohol to cations was suggested by EXAFS analysis. XANES analysis was useful in corroborating the EXAFS information and in providing information about the ionic character of the nearest-neighbor bonding.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01451546

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

4

Digitale Medien

Improved materials for blood-contacting applications: blends of sulphonated and non-sulphonated polyurethanes (1992)

Hergenrother, R. W. ; Cooper, S. L.

Springer

Journal of materials science 3 (1992), S. 313-321

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1573-4838

Quelle: Springer Online Journal Archives 1860-2000

Thema: Medizin , Technik allgemein

Notizen: Abstract Propyl sulphonate groups were grafted on to the urethane nitrogens of Pellethane 2363-80A at three levels: 1.2, 14, and 50%. Blends with an effective level of 1.2 and 14% were made by blending the 14 and 50% sulphonated polyurethanes with the unsubstituted material. Tensile testing was performed on the materials in both their dry and hydrated state. The blend materials exhibited a small improvement in tensile strength over their bulk analogues. Dynamic contact angle and X-ray photoelectron spectroscopy (XPS) showed an enrichment of sulphonate groups at the surface of the blend materials compared to bulk samples of the same overall composition. Canineex vivo shunt experiments revealed fewer platelets adherent and less platelet spreading on the blend materials than on the bulk materials with the same level of sulphonation. This suggests that sulphonated polyurethanes can be developed that have improved blood compatibility while maintaining good physical properties in an aqueous environment.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00705361

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

5

Digitale Medien

Ex-vivo blood compatibility of silicone-containing biomaterials (1994)

Lin, Horng-Ban ; Hergenrother, R. W. ; Silver, J. H. ; [weitere]

Springer

Journal of materials science 5 (1994), S. 207-213

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1573-4838

Quelle: Springer Online Journal Archives 1860-2000

Thema: Medizin , Technik allgemein

Notizen: The acute blood-contacting properties of five silicone-containing elastomers and a poly(vinyl alcohol) coated silicone elastomer were assessed using a canine ex vivo shunt model. The silicone-containing elastomers studied included two thermoset amorphous silica reinforced dimethyl methylvinyl siloxane-based polymers which were extruded as Silastic® RX-50 Medical Grade Tubing (RX-50) and Silastic® Medical Grade Tubing H.P. (HP). They also included three experimental thermoplastic silicone-urea urethane copolymers received as X7-4074 (SP-1), X7-4037 (SP-2), and X7-4943 (SP-3). The RX-50 tubing material showed less thrombus deposition compared to the silicone-urea urethane copolymers. This suggests that the blood-contacting response of a silicone elastomer is strongly affected by the incorporation of the urea urethane segments. Among the silicone-urea urethane copolymers, the SP-3 material showed higher levels of platelet and fibrinogen deposition than the SP-1 and SP-2 materials, whereas the SP-1 and SP-2 samples had similar levels of deposition. These results indicate that the blood-contacting properties of the silicone-urea urethane copolymers were influenced more by the molecular weight of the polydimethylsiloxane than by the type of diol used in the urea urethane segments. The maximal platelet deposition on the poly vinyl alcohol-coated silicone was approximately an order of magnitude greater than those on the silicone-containing elastomers indicating that the PVA coating was more thrombogenic.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00121090

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

6

Digitale Medien

Chemiluminescent oxidative products generated by in vitro leukocyte-material interactions (1996)

Lim, F. ; Cooper, S. L.

Springer

Journal of materials science 7 (1996), S. 69-76

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1573-4838

Quelle: Springer Online Journal Archives 1860-2000

Thema: Medizin , Technik allgemein

Notizen: The effect of different polymeric materials on leukocyte adhesion and their oxidative responses was investigated. Two commercial polymers: polyethylene (PE) and silicone rubber (SR) and two laboratory-synthesized polyurethanes were examined. The polyurethanes studied consisted of a polytetramethylene oxide (PTMO)-based polyurethane (PEU-base) and a sulfonated polyurethane (PEU-SO3). In vitro polymorphonuclear leukocyte (PMN) adhesion and respiratory burst activity measurements were studied using a radiolabelling technique and a chemiluminescence (CL) assay, respectively. An increased number of adherent PMNs and increased cell spreading were found on PEU-SO3 compared to the PEU-base, SR and PE. The largest CL response was also found on PEU-SO3, whereas on the other hydrophobic polymers the response was smaller. Additionally, on the PEU-SO3 surface the CL response was sustained indicating more prolonged production of oxygen radicals by PMNs on this material. Upon stimulation with opsonized zymosan (OZ), the PMNs on PEU-SO3 showed the lowest CL response, indicating a decreased respiratory burst differences among them in their CL response. The residual CL response was reduced by 30% for PEU-SO3 and by 10–15% for PE, SR and PEU-base compared to the control (luminometer polystyrene cuvette only, no disc). Upon addition of phorbol myristate acetate (PMA), all surfaces except SR showed a slightly reduced CL response. Along with PE, PEU-SO3 showed the lowest CL response. These results suggest that oxygen radicals are produced during early incubation of PMNs with biomaterials, and upon subsequent stimulation of these cells, fewer oxygen radicals are produced due to cellular exhaustion.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00058717

Permalink

	Standort	Signatur	Erwartet	Verfügbarkeit

Andere fanden auch interessant ...

Artikel (Nationallizenzen)

Volltext

7

Digitale Medien

A dielectric study of the glass transition region in segmented polyether-urethane copolymers (1983)

Vallance, M. A. ; Yeung, A. S. ; Cooper, S. L.

Springer

Colloid & polymer science 261 (1983), S. 541-554

zur Merkliste hinzufügen auf der Merkliste

Details

ISSN: 1435-1536

Schlagwort(e): Segmented polyurethanes ; dielectric relaxation ; crystallization ; microphase separation ; DSC

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau

Notizen: Abstract Ten polyether-urethane thermoplastic elastomers of varying chemical structure have been characterized by dielectric spectroscopy and scanning calorimetry. In the temperature range corresponding to the glass-rubber transition of the predominantly polyether phase, modification of the primary dielectric transition and the occurrence of a second transition at somewhat higher temperature have been observed. Through comparison with calorimetric data, these events have been related to supercooling of crystallizable polyether segments. Supercooling suppresses dielectric loss processes in some regimes and enhances losses in others. By systematic variation of chemical structure these phenomena have been classified.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01526619

Permalink