The impact of active and passive investment on market efficiency: a simulation study

We create a simulated financial market and examine the effect of different levels of active and passive investment on fundamental market efficiency. In our simulated market, active, passive, and random investors interact with each other through issuing orders. Active and passive investors select their portfolio weights by optimizing Markowitz-based utility functions. We find that higher fractions of active investment within a market lead to an increased fundamental market efficiency. The marginal increase in fundamental market efficiency per additional active investor is lower in markets with higher levels of active investment. Furthermore, we find that a large fraction of passive investors within a market may facilitate technical price bubbles, resulting in market failure. By examining the effect of specific parameters on market outcomes, we find that that lower transaction costs, lower individual forecasting errors of active investors, and less restrictive portfolio constraints tend to increase fundamental market efficiency in the market

Hepatotoxic substance(s) removed by high-flux membranes enhances the positive acute phase response

Hepatotoxic substance(s) removed by high-flux membranes enhances the positive acute phase response.BackgroundAcute phase proteins (APPs) are enhanced in end-stage renal disease patients (ESRD) requiring dialysis treatment. They are involved in a variety of pathologic processes like muscle proteolysis, cachexia, regulation of appetite, and atherosclerosis. They are predictive for mortality. APPs are not only makers but also active substances. They are mainly produced in liver cells and are primarily, but not exclusively, regulated by proinflammatory cytokines. To what extent hepatic APPs are influenced by uremic toxins is still unclear. Therefore, we investigated the effects of different ultrafiltrates (UFs) on the synthesis of α1-acid glycoprotein (AGP) in HepG2 cells.MethodsA cross-sectional as well as a crossover study with high-/low-flux membranes was conducted to investigate the impact of UFs on bioactivity of liver cell cultures. Metabolic activity (MTT test), cytotoxicity (lactate dehydrogenase release), and the positive APP AGP were measured in HepG2 cells.ResultsCultured hepatocytes treated with UFs from high-flux membranes exhibited a higher cytotoxicity (18.6 ± 0.3% high-flux vs. 13.9 ± 0.2% low-flux, P < 0.001) and a lower metabolic activity (29.3% high-flux vs. 50.3% low-flux, P < 0.001) in comparison with low-flux UFs. In addition, enhanced APP secretion could be observed under costimulatory conditions (high-flux 5.0 ± 0.7 vs. low-flux 3.1 ± 0.6 ng/μg protein, P < 0.05). The effects of high- and low-flux UFs were strongly expressed at the beginning and were still significantly different after 120 minutes of hemodialysis (HD) treatment. The cross-over experiments confirmed that UFs collected during high-flux HD had a higher capacity to stimulate AGP synthesis in liver cells.ConclusionThe effects of UFs from dialysis patients demonstrate that hepatotoxic substances can be removed by dialysis. Stimulating the acute phase response UF collected during high-flux HD had a higher impact on liver cells in comparison with low-flux UF. These substances are putative cofactors involved in cytokine regulation

Manufacturing conditioned wear of all-ceramic knee prostheses

To date, bioceramics have not been applied successfully in total knee joint endoprostheses. Sintered bioceramics can be machined only by grinding and polishing processes. Due to high quality requirements, there are significant challenges with regard to these machining technologies. An automated precise economical process chain for the manufacturing of a new all-ceramic knee implant design was developed. It was assumed the geometrical accuracy and the shape of implant contact geometry specified during the manufacturing process has a substantial influence on the wear behavior of the prosthesis. The importance of the surface quality of the ceramic implant surface remains unclear and warrants future examination

Manufacturing conditioned roughness and wear of biomedical oxide ceramics for all-ceramic knee implants

Background: Ceramic materials are used in a growing proportion of hip joint prostheses due to their wear resistance and biocompatibility properties. However, ceramics have not been applied successfully in total knee joint endoprostheses to date. One reason for this is that with strict surface quality requirements, there are significant challenges with regard to machining. High-toughness bioceramics can only be machined by grinding and polishing processes. The aim of this study was to develop an automated process chain for the manufacturing of an all-ceramic knee implant. Methods: A five-axis machining process was developed for all-ceramic implant components. These components were used in an investigation of the influence of surface conformity on wear behavior under simplified knee joint motion. Results: The implant components showed considerably reduced wear compared to conventional material combinations. Contact area resulting from a variety of component surface shapes, with a variety of levels of surface conformity, greatly influenced wear rate. Conclusions: It is possible to realize an all-ceramic knee endoprosthesis device, with a precise and affordable manufacturing process. The shape accuracy of the component surfaces, as specified by the design and achieved during the manufacturing process, has a substantial influence on the wear behavior of the prosthesis. This result, if corroborated by results with a greater sample size, is likely to influence the design parameters of such devices.DFG/CRC/59

Theoretical investigation of carbon defects and diffusion in α-quartz

The geometries, formation energies, and diffusion barriers of carbon point defects in silica (α-quartz) have been calculated using a charge-self-consistent density-functional based nonorthogonal tight-binding method. It is found that bonded interstitial carbon configurations have significantly lower formation energies (on the order of 5 eV) than substitutionals. The activation energy of atomic C diffusion via trapping and detrapping in interstitial positions is about 2.7 eV. Extraction of a CO molecule requires an activation energy <3.1 eV but the CO molecule can diffuse with an activation energy <0.4 eV. Retrapping in oxygen vacancies is hindered—unlike for O2—by a barrier of about 2 eV

Wear behaviour of filled polymers

Zur Verbesserung des Verschleißverhaltens von Nanokompositen auf Basis von Polyurethan (PU) wurde der Einfluss von ZrO2- und FeOx-Partikeln in Abhängigkeit von Partikelgröße und Partikelgehalt untersucht. Es zeigte sich bei beiden Partikelarten, dass ein zunehmender Partikelgehalt zu einer Erhöhung des Elastizitätsmoduls führte, wodurch die Materialbelastung stieg und der Verschleißkoeffizient zunahm. Mit zunehmender Partikelgröße nahm die Wechselwirkung der Oberflächenmodifikatoren mit der PU-Matrix ab. Dies führte bei den ZrO2- wie auch bei den FeOx-Kompositen mit den jeweils größten Partikeln dazu, dass eine Schubbelastung im wesentlichen durch die PU-Matrix aufgenommen wurde, wodurch es durch die gegenüber den Kompositen höhere Zähigkeit des PU wieder zu einer Abnahme des Verschleißkoeffizienten kam. In einer Finite-Elemente-Simulation konnte gezeigt werden, dass sich die elastische Dehnungsenergiedichte der Komposite umgekehrt zum Verschleißkoeffizienten verhielt. Dies zeigte, dass eine Verschleißzunahme bei zunehmendem Füllgrad durch eine Abnahme des elastischen Materialverhaltens der Komposite begründet war. Weiterhin wurden für ZrO2- und FeOx-Komposite die Oberflächenmodifikatoren variiert. Dabei konnten bei den ZrO2-Kompositen der Dispergierzustand, die Zahl der Anbindungen an die PU-Matrix und das Modifikationsverfahren als wichtige Einflussgrößen auf ein gutes Verschleißverhalten identifiziert werden. Bei den FeOx-Kompositen waren hierfür der Dispergierzustand, kurze Seitenketten und die Elektronegativität des an das Partikel anbindenden Atoms von Bedeutung.With the aim to improve the wear behaviour of nanoparticular reinforced polyurethanes the influence of particle size and particle content of ZrO2 and iron oxides were investigated. For both kinds of particles it was found that an increasing particle content led to an increase of the Youngs module as a result of which the material load increased and the wear coefficient increased. By an increasing particle size the interaction of the surface modificator decreased. This has caused for composites reinforced by ZrO2 as well as for the composites reinforced by iron oxides that the shear loads of the wear tests were to bear mainly by the polyurethan matrix material, and the wear coefficient decreased. In a finite element analysis it was shown that the composites have an increasing elastic strain energy density with decreasing wear coefficient. This shows the role of the elastic material behaviour on the increasing wear with increasing filler content. For the ZrO2 and iron oxid composites a variation of the surface modificator was performed. For ZrO2 composites it was found that the good state of dispersion, the number of bonds of the modificator molecules to the polyurethane matrix and the method of incorporating the modificator into the matrix are important influence factors on good wear behaviour. For the iron oxide composites a good state of dispersion, short side chains and the electronegativity of the bonding atom were found as important factors on good wear behaviour

Femtosecond time-resolved optical pump-probe spectroscopy at kilohertz-scan-rates over nanosecond-time-delays without mechanical delay line

We demonstrate a technique for femtosecond time-resolved optical pump-probe spectroscopy that allows to scan over a nanosecond time delay at a kilohertz scan rate without mechanical delay line. Two mode-locked femtosecond lasers with approximately 1 GHz repetition rate are linked at a fixed difference frequency of ΔfR=11 kHz. One laser delivers the pump pulses, the other provides the probe pulses. The relative time delay is linearly ramped between zero and the inverse laser repetition frequency at a rate ΔfR, enabling high-speed scanning over a 1 ns time delay. The advantages of this method for all-optical pump-probe experiments become evident in an observation of coherent acoustic phonons in a semiconductor superlattice via transient reflectivity changes. A detection shot-noise limited signal resolution of 7×10 8 is obtained with a total measurement time of 250 s. The time resolution is 230 fs