Hochvernetzte Poyethylene in der Hüftendoprothetik

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die Notwendigkeit künstlicher Hüftgelenke nimmt mit dem steigenden Durchschnittsalter der Bevölkerung zu. Etwa 0,1% der Bevölkerung der Welt mit „westlicher" Lebensweise benötigt ein künstliches Hüftgelenk. Die derzeit verwendeten Werkstoffe in der Hüftendoprothetik besitzen, trotz stetiger Verbesserungen, immer noch zu hohe Abriebswerte. Somit ist das Hauptziel der heutigen Forschung über Werkstoffe für die Endoprothetik, Reibungsparmer zu finden, die über einen langfristigen Zeitraum weniger Verschleiß aufweisen, bei gleichzeitiger Biokompatibilität. Derzeit ist häufig von XPE (hochvernetztes UHMW-PE) die Rede. Die sehr guten Abriebswerte von XPE geben Anlaß zu Hoffnung, ein geeignetes Material gefunden zu haben. Aber wie sieht es mit den anderen Eigenschaften aus? Unterschiedlichste Herstellungs- und Prüfmethoden erschweren den direkten Vergleich der Eigenschaften. XPE kann entweder durch Bestrahlung von UHMW-PE hergestellt werden, oder durch chemische Reaktionen mittels organischen Peroxiden. Bei der Bestrahlung können entweder Gammastrahlen oder Elektronenstrahlen zum Einsatz kommen. Die chemische Herstellung spielt im Moment noch keine große Rolle und wird deshalb im Folgenden nicht näher behandelt. In dieser Arbeit wurde versucht, aus bereits unternommenen Studien Tendenzen ableiten zu können, ob XPE den Erwartungen entspricht

Radium single-ion optical clock

We explore the potential of the electric quadrupole transitions 7s\,^2S_{1/2} - 6d\,^2D_{3/2}, 6d\,^2D_{5/2} in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition 7s\,^2S_{1/2}\,(F=2,m_F=0) - 6d\,^2D_{3/2}\,(F=0,m_F=0) at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.Comment: 20 pages, 1 figur

Preference of Xenopus laevis for different housing conditions

Since the European frogs (Rana spp.) have been included in the German endangered species regulations, Xenapus Laevis (South African Clawed Frog) is being used increasingly in animal research and in teaching. In this study, the preference ofX. laevis for different housing conditions were examined. X. laevis preferred dark backgrounds, a water temperature between 20C-22C and the deeper parts of the test basin Red earthenware pipe was accepted as cover transparent pipe was not. The frogs avoided areas illuminated with more than 200 lux

Rigorous results on spontaneous symmetry breaking in a one-dimensional driven particle system

We study spontaneous symmetry breaking in a one-dimensional driven two-species stochastic cellular automaton with parallel sublattice update and open boundaries. The dynamics are symmetric with respect to interchange of particles. Starting from an empty initial lattice, the system enters a symmetry broken state after some time T_1 through an amplification loop of initial fluctuations. It remains in the symmetry broken state for a time T_2 through a traffic jam effect. Applying a simple martingale argument, we obtain rigorous asymptotic estimates for the expected times ~ L ln(L) and ln() ~ L, where L is the system size. The actual value of T_1 depends strongly on the initial fluctuation in the amplification loop. Numerical simulations suggest that T_2 is exponentially distributed with a mean that grows exponentially in system size. For the phase transition line we argue and confirm by simulations that the flipping time between sign changes of the difference of particle numbers approaches an algebraic distribution as the system size tends to infinity.Comment: 23 pages, 7 figure

The political economy of international factor mobility

We model the endogenous determination of policy towards international factor mobility. In a common agency setting, domestic interest groups bid for protection from the government and the incumbent politicians maximize a welfare function that depends both on domestic voters\u2019 welfare and contributions collected. We characterize equilibrium policies in the price space and show how the degree of complementarity among inputs determines the outcome. We establish a similar result for quotas, allowing for partial rent capturing. For the strategic environment under consideration, we also establish a general equivalence result between tariffs and quotas if capturing is complete

Dynamic correlation functions and Boltzmann Langevin approach for driven one dimensional lattice gas

We study the dynamics of the totally asymmetric exclusion process with open boundaries by phenomenological theories complemented by extensive Monte-Carlo simulations. Upon combining domain wall theory with a kinetic approach known as Boltzmann-Langevin theory we are able to give a complete qualitative picture of the dynamics in the low and high density regime and at the corresponding phase boundary. At the coexistence line between high and low density phases we observe a time scale separation between local density fluctuations and collective domain wall motion, which are well accounted for by the Boltzmann-Langevin and domain wall theory, respectively. We present Monte-Carlo data for the correlation functions and power spectra in the full parameter range of the model.Comment: 10 pages, 9 figure

Phase-separation transition in one-dimensional driven models

A class of models of two-species driven diffusive systems which is shown to exhibit phase separation in d=1 dimensions is introduced. Unlike previously studied models exhibiting similar phenomena, here the relative density of the two species is fluctuating within the macroscopic domain of the phase separtated state. The nature of the phase transition from the homogeneous to the phase-separated state is discussed in view of a recently introduced criterion for phase separation in one-dimensional driven systems

Aspects of Cooling at the TRIμ\muP Facility

The Tri$\mu$P facility at KVI is dedicated to provide short lived radioactive isotopes at low kinetic energies to users. It comprised different cooling schemes for a variety of energy ranges, from GeV down to the neV scale. The isotopes are produced using beam of the AGOR cyclotron at KVI. They are separated from the primary beam by a magnetic separator. A crucial part of such a facility is the ability to stop and extract isotopes into a low energy beamline which guides them to the experiment. In particular we are investigating stopping in matter and buffer gases. After the extraction the isotopes can be stored in neutral atoms or ion traps for experiments. Our research includes precision studies of nuclear $\beta$-decay through $\beta$-$\nu$ momentum correlations as well as searches for permanent electric dipole moments in heavy atomic systems like radium. Such experiments offer a large potential for discovering new physics.Comment: COOL05 Workshop, Galena, Il, USA, 18-23. Sept. 2005, 5 pages, 3 figure

Изучение методики статистической обработки экспериментальных данных

Методические указания к лабораторной работе № 1 «Изучение методики статистической обработки экспериментальных данных » по разделу «Физические основы механики» курса физики для студентов всех специальностей

Spontaneous Symmetry Breaking in a Non-Conserving Two-Species Driven Model

A two species particle model on an open chain with dynamics which is non-conserving in the bulk is introduced. The dynamical rules which define the model obey a symmetry between the two species. The model exhibits a rich behavior which includes spontaneous symmetry breaking and localized shocks. The phase diagram in several regions of parameter space is calculated within mean-field approximation, and compared with Monte-Carlo simulations. In the limit where fluctuations in the number of particles in the system are taken to zero, an exact solution is obtained. We present and analyze a physical picture which serves to explain the different phases of the model