Effective Spin Models for Spin-Phonon Chains by Flow Equations

We investigate the anti-adiabatic limit of an anti-ferromagnetic S=1/2 Heisenberg chain coupled to Einstein phonons. The flow equation method is used to decouple the spin and the phonon part of the Hamiltonian. In the effective spin model long range spin-spin interactions are generated. We determine the phase transition from a gapless state to a gapped (dimerised) phase, which occurs at a non-zero value of the spin-phonon coupling. In the effective phonon sector a phonon hardening is observed.Comment: RevTeX, 6 pages, 4 eps figures; final version containing some clarification

Keramikfrakturen verschraubter Implantatbrücken unter zyklischer Belastung

Introduction: In implant prosthodontics, fixed dental prostheses (FDP) can either be screw retained or cement retained. Screw retention provides in general the possibility of retrieving the restoration. In former studies it could be shown that more chipping fractures of the ceramic occur on the occlusal surface of screw retained implant supported restorations with unfilled screw access holes than in cemented restorations. The ceramic in the surrounding area of the screw access hole seems to be the weakest point of the veneer ceramic. The purpose of this study was to investigate the effects of dynamic loading on the veneer ceramic around the screw access holes. The aim was to prove if an adhesive filling of the screw access hole would reduce the number of occlusal chipping fractures. Material and methods: For a three implant situation 20 screw-retained ceramic veneered five-unit FDPs were fabricated. The FDPs were divided into two groups. For the first group the screw access holes remained unfilled and for the second group the screw access holes were restored with an adhesive composite resin restoration. A mastication simulator was used for axial loading to the implant positions for 20.000 cycles with individual adjusted antagonists. Every load-cycle applied a force of 100 N for two seconds followed by one second of relieve. Three clinicians evaluated the chipping fractures using a light microscope and a dental probe. For the statistical comparison of the two different groups, the numbers of chipping fractures found were analysed using a generalized linear model with Poisson response and log link function. The level of significance was set to a = .05. Results: Significantly more chipping fractures occurred in the group of screw-retained FDPs with unfilled screw access holes. The rate ratio of unrestored versus restored FDPs was 3.287 with a P-value of .006. It could be proved that an adhesive composite resin restoration of the screw access hole significantly reduces occlusal chipping fractures. Discussion: The three investigators independently detected a significant difference between screw-retained ceramic veneered implant superstructures with restored and unrestored screw access holes. Under observation of the number of chipping fractures, the hypothesis that an adhesive composite resin filling reduces the fragility of the occlusal veneer ceramic could be confirmed. Although the three investigators evaluated the chipping fractures differently, all three of them found less chipping fractures on the FDPs with the adhesive restored screw access holes.Einleitung: In der Implantatprothetik können festsitzende Restaurationen entweder verschraubt oder zementiert werden. Die Verschraubung gewährleistet grundsätzlich die Möglichkeit der Wiederabnahme der Restauration. In früheren Untersuchungen an verschraubten Brücken konnte bereits gezeigt werden, dass okklusale Keramikabplatzungen generell häufiger auftreten als bei zementierten Restaurationen. Die Verblendkeramik in direkter Umgebung der Schraubenzugangsöffnung scheint dabei besonders gefährdet zu sein. In der vorliegenden Studie wurde die Auswirkung von zyklischer Belastung auf den Bereich der Keramikverblendung um die Schraubenöffnung analysiert. Es sollte gezeigt werden, ob durch einen adhäsiven Verschluss der Zugangsöffnung die Anzahl der okklusalen Abplatzungen reduziert werden kann. Material und Methode: Für eine Modellsituation mit drei Implantaten wurden 20 fünfgliedrige keramikverblendete verschraubte Brücken hergestellt. Diese wurden in zwei Gruppen unterteilt. Bei zehn Brücken blieben die Schraubenzugangsöffnungen ungefüllt, die anderen zehn wurden mittels einer ad-häsiven Kunststofffüllung verschlossen. Im Kausimulator durchlief jede Brücke 20.000 Belastungszyklen. Mittels individuell angepasster Antagonisten wurden die Suprakonstruktionen axial zu den Implantat-Positionen belastet. Jeder dieser Zyklen bestand aus einer Belastungsphase mit einer ansteigenden Kraft bis 100 N für die Dauer von zwei Sekunden und einer Entlastungsphase von einer Sekunde. Nach Abschluss der Kausimulation begutachteten drei Kliniker die Brücken lichtmikroskopisch auf Abplatzungen, wobei die Keramikschulter um die Schraubenöffnung sondiert wurde. Zum statistischen Vergleich der beiden Brückengruppen wurde ein generali-siertes lineares Modell mit der Anzahl der Abplatzungen als Poisson-verteilte Responsevariable verwendet. Die Berechnungen wurden mit einem Signifikanzniveau von α = .05 durchgeführt. Ergebnisse und Beobachtungen: Die Anzahl von Keramikabplatzungen in der Brückengruppe mit den ungefüllten Schraubenöffnungen war signifikant höher als in der Gruppe mit den gefüllten Schraubenzugängen. Das Verhältnis der Abplatzungen an den ungefüllten Schraubenöffnungen zu den gefüllten betrug 3.287 bei einem P- Wert von .006. Es konnte gezeigt werden, dass sich das Auftreten von Keramikfrakturen in der direkten Umgebung des Schraubenlochs mit einer adhäsiven Kunststofffüllung signifikant reduzieren lässt. Diskussion: Es wurde von allen drei Untersuchern unabhängig voneinander ein signifikanter Unterschied zwischen den verschraubten, keramikverblendeten Implantatsuprakonstruktionen mit adhäsiv gefüllten und ungefüllten Schraubenzugangsöffnungen festgestellt. Die Hypothese, dass die adhäsive Füllung der okklusalen Schraubenzugangsöffnung die Frakturanfälligkeit der Keramik reduziert, konnte unter Beachtung der Anzahl der okklusalen Keramikabplatzungen bestätigt werden. Obwohl die drei Untersucher die Abplatzungen unterschiedlich bewerteten, fanden alle drei weniger Keramikabplatzungen an den verschraubten Brücken mit den adhäsiv gefüllten Schraubenzugangsöffnungen

Die Entwicklung dielektrischer Eigenschaften in Metall- und Halbleiterclustern

Im Rahmen dieser Arbeit werden Metall- und Halbleitercluster hinsichtlich ihrer geometrischen und elektronischen Struktur eingehend untersucht. Die zentrale experimentelle Methode ist die Molekularstrahlablenkung im elektrischen Feld. Aus diesem Experiment werden die permanenten Dipolmomente und Polarisierbarkeiten der Cluster gewonnen. In Verbindung mit verschiedenen quantenchemischen Methoden werden diese zur Strukturaufklärung neutraler Silicium- und Bleiclustern verwendet. Für letztere kann dies erstmals bis zum Pb36-Cluster durchgeführt werden. Damit wird der im Rahmen dieser Methode erfassbare Größenbereich erheblich ausgedehnt und gleichzeitig eine technische Grenze des Verfahrens erreicht. Sowohl Blei- als auch Siliciumcluster verändern mit zunehmender Größe ihre Wachstumsmuster. Siliciumcluster sind bis etwa Si30 prolat, bevor sie zu sphärischen Strukturen übergehen. Dies spiegelt sich dramatisch in den dielektrischen Eigenschaften wider und kann erstmals durch Ablenkmessungen bis Si75 nachvollzogen werden. Bleicluster wachsen in Strukturen, die bevorzugt Pb7-Einheiten in Form pentagonaler Bipyramiden enthalten. Die starke Elektronenlokalisation in diesen Untereinheiten führt dazu, dass Bleicluster bis mindestens Pb36 nicht-metallischen Charakter haben

Control of TRPM3 Ion Channels by Protein Kinase CK2-Mediated Phosphorylation in Pancreatic β-Cells of the Line INS-1

In pancreatic β-cells of the line INS-1, glucose uptake and metabolism induce the openings of Ca2+-permeable TRPM3 channels that contribute to the elevation of the intracellular Ca2+ concen tration and the fusion of insulin granules with the plasma membrane. Conversely, glucose-induced Ca2+ signals and insulin release are reduced by the activity of the serine/threonine kinase CK2. There fore, we hypothesized that TRPM3 channels might be regulated by CK2 phosphorylation. We used recombinant TRPM3α2 proteins, native TRPM3 proteins from INS-1 β-cells, and TRPM3-derived oligopeptides to analyze and localize CK2-dependent phosphorylation of TRPM3 channels. The func tional consequences of CK2 phosphorylation upon TRPM3-mediated Ca2+ entry were investigated in Fura-2 Ca2+-imaging experiments. Recombinant TRPM3α2 channels expressed in HEK293 cells displayed enhanced Ca2+ entry in the presence of the CK2 inhibitor CX-4945 and their activity was strongly reduced after CK2 overexpression. TRPM3α2 channels were phosphorylated by CK2 in vitro at serine residue 1172. Accordingly, a TRPM3α2 S1172A mutant displayed enhanced Ca2+ entry. The TRPM3-mediated Ca2+ entry in INS-1 β-cells was also strongly increased in the presence of CX-4945 and reduced after overexpression of CK2. Our study shows that CK2-mediated phosphorylation controls TRPM3 channel activity in INS-1 β-cells

Understanding the dynamics of randomly positioned dipolar spin ensembles

Dipolar spin ensembles with random spin positions attract much attention currently because they help to understand decoherence as it occurs in solid state quantum bits in contact with spin baths. Also, these ensembles are systems which may show many-body localization, at least in the sense of very slow spin dynamics. We present measurements of the autocorrelations of spins on diamond surfaces in a doubly-rotating frame which eliminates local disorder. Strikingly, the time scales in the longitudinal and the transversal channel differ by more than one order of magnitude which is a factor much greater than one would have expected from simulations of spins on lattices. A previously developed dynamic mean-field theory for spins (spinDMFT) fails to explain this phenomenon. Thus, we improve it by extending it to clusters (CspinDMFT). This theory does capture the striking mismatch up to two orders of magnitude for random ensembles. Without positional disorder, however, the mismatch is only moderate with a factor below 4. The pivotal role of positional disorder suggests that the strong mismatch is linked to precursors of many-body localization.Comment: 21 pages, 12 figure

Understanding the dynamics of randomly positioned dipolar spin ensembles

Dipolar spin ensembles with random spin positions are attracting much attention because they help us to understand decoherence as it occurs in solid-state quantum bits in contact with spin baths. Also, these ensembles are systems which may show many-body localization, at least in the sense of very slow spin dynamics. We present measurements of the autocorrelations of spins on diamond surfaces at infinite temperature in a doubly rotating frame which eliminates local disorder. Strikingly, the timescales in the longitudinal and the transversal channel differ by more than one order of magnitude, which is a factor much greater than one would have expected from simulations of spins on lattices. A previously developed dynamic mean-field theory for spins (spinDMFT) fails to explain this phenomenon. Thus, we improve it by extending it to clusters (CspinDMFT). This theory does capture the striking mismatch up to two orders of magnitude for random ensembles. Without positional disorder, however, the mismatch is only moderate with a factor below 4. The pivotal role of positional disorder suggests that the strong mismatch is linked to precursors of many-body localization

Palaeoenvironmental changes recorded in the palynology and palynofacies of a Late Permian Marker Mudstone (Galilee Basin, Australia)

Reconstructing the terrestrial palaeoenvironment during the end-Permian is made challenging by widespread erosion and ecosystem destruction. High-resolution sampling for palynofacies and palynology in sections that preserve the boundary interval allows for detailed examination of the drastic environmental changes that characterize the Permian–Triassic mass extinction. In the Bowen and Galilee basins in eastern Australia, this environmental perturbation is recorded within a Marker Mudstone that occurs above the uppermost Permian coal seams. The Marker Mudstone is used as a stratigraphic reference level at many localities, but has previously only been studied at a single locality in the Bowen Basin. In the present study, borehole Tambo 1-1A drilled in the Galilee Basin was selected to clarify whether this black, organic-rich mudstone marks a marine transgression, and to examine potential indicators of the end-Permian mass extinction. A total of 22 samples were taken from the mudstone unit, and from the over- and underlying strata and processed for palynology, palynofacies, and carbon isotope analysis. Biostratigraphic data indicate that the Marker Mudstone itself covers the uppermost part of unit APP5, with the first index taxa of unit APP6 floras occurring in samples less than 80 cm above this interval. This can be correlated with several other localities in the Bowen and Sydney basins where this shift occurs just above the uppermost Permian coal seam. Palynofacies data agree with previous interpretations of a southwards prograding delta that subsides as base level rises to form an extensive waterbody in which the Marker Mudstone was deposited. A change from translucent phytoclast-dominated to opaque phytoclast-dominated palynofacies within the Marker Mudstone suggests a shift to more oxic conditions in the water column, while base level begins to fluctuate, or increased terrestrial input from fluvial systems as the hinterland rises. Algal bodies resembling Botryococcus are found in the strata above the Marker Mudstone, but differ in morphology from the algal bodies found in the deltaic facies below. The presence of acanthomorph acritarchs in the Marker Mudstone and in the overlying Rewan Formation may indicate marine influence. Forms resembling fungal spores are present, but they do not show a “spike” as seen in other P–T boundary localities. The relative position of unit APP6 to the P–T boundary itself remains unclear. APP6 assemblages are dominated by simple acavate trilete and cavate trilete spores, which suggests stressed environment dominated by ferns and lycopods. The presence of degraded phytoclasts towards the top of the Marker Mudstone may also be used to suggest a mass-extinction interval. They may also be indicative of shifting local palaeoenvironmental changes, an interpretation that is supported by the low magnitude negative excursion of the δC isotope values within the Marker Mudstone. More datasets from the Bowen and Galilee basins will be essential to decoupling these signals

The Impact of Bioactive Lipids on Cardiovascular Development

Lysophospholipids comprise a group of bioactive molecules with multiple biological functions. The cardinal members of this signalling molecule group are sphingosylphosphorylcholine (SPC), lysophosphatidic acid (LPA), and sphingosine 1-phosphate (S1P) which are, at least in part, homologous to each other. Bioactive lipids usually act via G-protein coupled receptors (GPCRs), but can also function as direct intracellular messengers. Recently, it became evident that bioactive lipids play a role during cellular differentiation development. SPC induces mesodermal differentiation of mouse ES cells and differentiation of promyelocytic leukemia cells, by a mechanism being critically dependent on MEK-ERK signalling. LPA stimulates the clonal expansion of neurospheres from neural stem/progenitor cells and induces c-fos via activation of mitogen- and stress-activated protein kinase 1 (MSK1) in ES cells. S1P acts on hematopoietic progenitor cells as a chemotactic factor and has also been found to be critical for cardiac and skeletal muscle regeneration. Furthermore, S1P promotes cardiogenesis and similarly activates Erk signalling in mouse ES cells. Interestingly, S1P may also act to maintain human stem cell pluripotency. Both LPA and S1P positively regulate the proliferative capacity of murine ES cells. In this paper we will focus on the differential and developmental impact of lysophospholipids on cardiovascular development