Search Results - (Author, Cooperation:J. Koepke)

2013-12-03

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-06-10

BMJ Publishing

2044-6055

Medicine

Open access, Epidemiology

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A diamond anvil high-pressure cell especially designed for single-crystal x-ray diffraction studies is described, and with its commercial STOE goniometer head the new cell fits to almost every diffractometer type in use. In this high-pressure cell the x-ray beam passes nearly perpendicular to the pressure generating force. This geometry also allows the cell to be used on Weissenberg cameras, but with double-radius film cylinders and adequately enlarged layer line screens. A knee-type lever arm system generates the thrust. In the path of the beams there are no longer larger beryllium parts, which has improved the signal-to-noise ratio. Approximately 90% of all possible non-Friedel reflections for Bragg angles up to 45° can be measured in the bisecting (cursive-theta=ω) position, up to 95% with general diffractometer settings. An analytic absorption correction was used with beryllium gasketing to eliminate the need to know the thickness of the gasket between the two diamonds. The highest pressure reached which gave satisfactory results was 2.3 GPa. Inconel gaskets were used to collect data at pressures up to 10.2 GPa. Corrections for shadowing by the beams of the cell, absorption, and overlapping of sample reflections from other single crystals inside the cell are calculated using a special control program.

Electronic Resource

0165-0327

(Discriminant analysis) ; Bipolar ; DSM-III ; Schizo-affective ; Schizo-depression ; Schizo-mania ; Unipolar

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Medicine

Psychology

Electronic Resource

0005-2728

(Rps. viridis) ; Membrane protein ; Photosynthesis ; Reaction center

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Medicine

Physics

Electronic Resource

0022-0248

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Geosciences

Physics

Electronic Resource

0167-2738

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

Electronic Resource

1436-6274

Schlüsselwörter Wirbelfrakturen ; Spongiosaplastik ; Korrekturverlust ; Transplantatnekrose ; Key words Spine fractures ; Bone graft ; Loss of correction ; Transplant necrosis

Springer Online Journal Archives 1860-2000

Medicine

In the treatment of thoracolumbar fractures of the spine an osteosynthesis in the real sense is not possible. The result of the injury is not only bony destruction but also in most cases biomechanical instability of the motion segment. The goal of operative treatment is stability. Besides internal fixation bone transplantation is necessary to achieve bony fusion. A common procedure is transpedicular bone grafting. Posterior stabilization with an internal fixator is combined with cancellous bone transplantation, which is placed into the vertebral body and the intervertebral space through the pedicles. Resection of the intervertebral disc is necessary to obtain bone healing under the protection of the implant. In a clinical study after the stabilizing operation, we found a correction loss of 30–60% that was independent of the fracture type, implant or operation procedure. The lack of healing of the bone graft was the reason for the correction loss. Besides the unfavorable vascularization of the intervertebral space which cannot be influenced by operation, the morphological arrangement and spatial expansion of the cancellous bone transplant are important for obtaining contact with the endplate of the cranially situated vertebral body. The assessment of the 3D reconstructions, generated from the digitized picture data of CT scans, shows small volumes of cancellous bone grafts with no or poor contact to the neighboring vertebral body. Our results indicate that transpedicular bone grafting cannot be recommended for the operative treatment of unstable thoracolumbar spinal fractures, since in most cases no bony fusion occurs. In our opinion combined anterior-posterior stabilizations are more often indicated.

In der operativen Behandlung instabiler Frakturen der thorakolumbalen Wirbelsäule ist eine Osteosynthese im eigentlichen Sinn nicht möglich. Bei der Verletzung tritt nicht nur ein isolierter knöcherner Schaden ein, sondern in den meisten Fällen auch eine biomechanische Instabilität des betroffenen Bewegungssegments. Das Ziel der operativen Behandlung besteht darin, Stabilität zu erzeugen. Neben der Instrumentation mit internen Fixationssystemen ist eine Knochentransplantation erforderlich, um eine knöcherne Spondylodese zu erzielen. Die häufigste Form der Knochentransplantation ist die transpedikuläre Spongiosaplastik, bei welcher im Rahmen der dorsalen Implantation des Fixateur interne über die Pedikel des Wirbels Spongiosa in den Wirbelkörper und den Intervertebralraum plaziert wird. Voraussetzung für die knöcherne Einheilung des Transplantats unter dem Schutz des stabilisierenden Implantats ist die vorherige Resektion des intervertebralen Bandscheibengewebes. In der klinischen Studie wurden Korrekturverluste in der Größenordnung von 30–60% im Bereich der operierten Bewegungssegmente unabhängig vom Frakturtyp, Implantat oder Operationsverfahren nachgewiesen. Verantwortlich war im wesentlichen die fehlende Einheilung der transplantierten Spongiosa. Neben der ungünstigen Vaskularisation im Intervertebralraum, welche operativ unbeeinflußbar ist, kommt der morphologischen Anordnung des Transplantats, seiner räumlichen Ausdehnung und damit der Möglichkeit, mit dem benachbarten Wirbel in Kontakt zu kommen, eine besondere Bedeutung zu. Die Auswertung von 3D-Rekonstruktionen, welche aus den CT-Bilddaten gewonnen wurden, zeigt unbefriedigend kleine Spongiosavolumina, die keinen oder eine nur ungenügenden Kontakt zum Nachbarwirbel herstellen. Die vorliegenden NMR-Untersuchungen belegen eine mangelnde Vitalität der transplantierten Spongiosa. Da überwiegend keine knöcherne Fusion von instabilen Bewegungssegmenten oder nur unter Entwicklung von erheblichen Korrekturverlusten eintritt, ist die transpedikuläre Spongiosaplastik nach den obigen Ergebnissen nicht für die operative Stabilisierung thorakolumbaler Frakturen geeignet. Als Konsequenz aus den Ergebnissen muß die Indikation zur kombiniert dorso-ventralen Stabilisierung häufiger gestellt werden. Möglicherweise werden in Zukunft endoskopische minimalinvasive Techniken weiter perfektioniert, um invasive, patientenbelastende Verfahren zu vermeiden und das Komplikationsrisiko zu senken.

Electronic Resource

1438-1168

Springer Online Journal Archives 1860-2000

Geosciences

Summary Late Cretaceous metamorphites, investigated in a profile near Lendas/Asterousia Mountains (southern coast of Crete), consist of the following lithological units (from the base to the top): massive ortho-amphibolites, which may contain diopside besides plagioclase and magnesiohornblende; cordierite-garnet-sillimanite-biotite gneisses; calc-silicate rocks and marbles with salitic pyroxene, pargasite, magnesio-homblende, cummingtonite, grossular-andradite garnet, wollastonite, and scapolite. Meta-ultramafics with anthophyllite, tremolite, olivine, and orthopyroxene are intercalated with the calc-silicate series. The mineral parageneses in the four classic bulk rock compositions — basic, pelitic, siliceous-calcareous, and ultrabasic — afford an opportunity to characterize the metamorphic facies in detail. From these parageneses, and from the Mg/Fe2+ ratios of coexisting cordierite and garnet, temperatures between 650 and 700°C and pressures between 4 and 6 kbar have been estimated for the conditions of metamorphism.

Zusammenfassung Zur Charakterisierung der Metamorphose-Fazies des oberkretazischen Kristallins wurde ein Profil bei Lendas im Asterousia-Gebirge an der Südküste Kretas gewählt. Der Kristallin-Komplex besteht dort — vom Liegenden zum Hangenden — aus massigen Ortho-Amphiboliten, die neben Plagioklas und Magnesiohornblende Diopsid enthalten können, aus Cordierit-Granat-Sillimanit-Biotit-Gneisen sowie aus einer kalksilikatischen Serie mit salitischem Pyroxen, Pargasit, Magnesiohornblende, Cummingtonit, Granat der Grossular-Andradit-Reihe, Wollastonit und Skapolith. In die kalksilikatische Serie sind Anthophyllit, Tremolit, Olivin und Orthopyroxen führende Meta-Ultrabasite eingeschaltet. Die Mineralparagenesen in den vier klassischen Stoffbeständen — basaltisch, pelitisch, kieselig-kalkig, ultrabasisch — ermöglichen eine detaillierte Charakterisierung der Metamorphose-Fazies. An Hand dieser Paragenesen und der Mg/Fe2+-Verhältnisse in Cordierit und Granat wurden für die Metamorphose Temperaturen zwischen 650 und 700°C und Drucke zwischen 4 und 6 kbar abgeschätzt.

Electronic Resource

1432-2021

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract An improved single-crystal high-pressure anvil cell with beryllium-gaskets was used for the investigations of structure and lattice parameters of cordierite which had been heated in an Ar stream at about 1,000° C to remove natural water from its structural channels. The influences of pressure transmitting media were studied by using water as a pressure medium at pressures of 0.3, 0.9, 1.2, and 2.3 GPa and fluorcarbon, a liquid consisting of large molecules, at 2.2 GPa. Water, but not fluorcarbon, is able to enter the channels in the cordierite structure. Large variations in the lattice constants resulted from changing the pressure medium used. A previously supposed discontinuity of the b lattice constant at nearly 0.3 GPa could not be established by the measurements taken so that there is no evidence for a phase transition at this pressure. Possibly the observed tilting of two tetrahedra against each other in this structure could have led to this misinterpretion. When water, but not fluorcarbon, is used as a pressure medium at 2.3 GPa, an additional electron density peak, presumably a water oxygen atom, appears in the channels. The water prevents the channels from shrinking and fixes their width at a value comparable to that of a naturally hydrated cordierite. In one of the silicate-tetrahedra the Si-O bond lengths are compressed almost 1 percent (2.3 GPa). This process may initiate a phase transition at higher pressures.

Electronic Resource