Effects of the physicochemical properties of titanium dioxide nanoparticles, commonly used as sun protection agents, on microvascular endothelial cells

Until now, the potential effects of titanium dioxide (TiO₂) nanoparticles on endothelial cells are not well understood, despite their already wide usage. Therefore, the present work characterizes six TiO₂ nanoparticle samples in the size range of 19 × 17 to 87 × 13 nm, which are commonly present in sun protection agents with respect to their physicochemical properties (size, shape, ζ-potential, agglomeration, sedimentation, surface coating, and surface area), their interactions with serum proteins and biological impact on human microvascular endothelial cells (relative cellular dehydrogenase activity, adenosine triphosphate content, and monocyte chemoattractant protein-1 release). We observed no association of nanoparticle morphology with the agglomeration and sedimentation behavior and no variations of the ζ-potential (?14 to ?19 mV) in dependence on the surface coating. In general, the impact on endothelial cells was low and only detectable at concentrations of 100 μg/ml. Particles containing a rutile core and having rod-like shape had a stronger effect on cell metabolism than those with anatase core and elliptical shape (relative cellular dehydrogenase activity after 72 h: 60 vs. 90 %). Besides the morphology, the nanoparticle shell constitution was found to influence the metabolic activity of the cells. Upon cellular uptake, the nanoparticles were localized perinuclearly. Considering that in the in vivo situation endothelial cells would come in contact with considerably lower nanoparticle amounts than the lowest-observable adverse effects level (100 μg/ml), TiO₂ nanoparticles can be considered as rather harmless to humans under the investigated conditions.     

Controlling the early stages of pentacene growth by supersonic molecular beam deposition

The key role of the pentacene kinetic energy (Ek) in the early stages of growth on SiOx/Si is demonstrated: islands with smooth borders and increased coalescence differ remarkably from fractal-like thermal growth. Increasing Ek to 6.4 eV, the morphology evolves towards higher density of smaller islands. At higher coverage, coalescence grows with Ek up to a much more uniform, less defected monolayer. The growth, interpreted by the diffusion mediated model, shows the critical nucleus changing from 3 to 2 pentacene for Ek>5-6 eV. Optimal conditions to produce single crystalline films are envisaged.     

The angular dependence of flux,mean energy and speed ratio for D2 molecules desorbing from a Ni(111) surface

Experimental data are presented for the angular dependence of the relative flux, the mean energy and the speed ratio of deuterium molecules desorbing from a Ni(111) crystal surface at a surface temperature of T_s = 1143 K and at sulphur coverages ranging between 30% and less than 2% of a monolayer.The angular flux distribution is sharply peaked in the forward direction (cos^dθwith 3 ? d ? 5) and the mean energy 〈E〉 of the desorbate depends strongly on the desorption angle θ. For normal desorption $\text{(θ = 0°)}\text{〈E〉}\text{2k}$ is about 700 K higher than T_s and for glancing angles (θ = 80°) it decreases to about 400 K below T_s The results obtained on sulphur free and sulphur covered Ni(111) surfaces are compared with our former data on polycrystalline nickel. The main differences in the kinetic features can be ascribed to the surface roughness. Accordingly, the angular distributions of flux, mean energy, and speed ratio, which deviate strongly from the Knudson and Maxwellian law, do not seem to depend considerably on sulphur coverage and surface structure. A qualitative explanation for these deviations is presented using the principle of detailed balancing.     

Zur Existenz von separablen stochastischen Prozessen

Ohne ZusammenfassungK. L. Chung und J. L. Doob haben bereits im April 1965 im wesentlichen die Aussage von Satz 2 für T=R in Proposition 33 ihrer Arbeit Fields, Optionality and Measurability, Amer. J. Math. 87, 397–424 (1965) mit Hilfe völlig anderer Methoden bewiesen. Dabei benutzen sie unser Kriterium (2.4) als Definition der SeparabilitÄt.     

Two-photon photoemission from Ni (1 1 0) and (1 1 1) surfaces

Photoemission was observed when the samples were irradiated with photons in the energy range from 2.5 to 3.3 eV from a tunable dye laser with an intensity of 10⁸Wcm^?2. The emission shows a quadratic intensity dependence. The variation with angle of incidence and polarization is different for the two surfaces. The result obtained from the (1 1 0) surface is discussed with help of the band structure as a two-photon surface photoelectric effect.     

Fast deuterium molecules desorbing from metals

The velocity distribution of D₂ desorbing from Pd(100) reveals the existence of two distinct groups of molecules, fast and slow ones. A new mechanism is proposed for the desorption of the molecules belonging to the fast group: after diffusing to the surface, absorbed D atoms recombine directly, without equilibrating in the chemisorption well. The fast molecules observed in the D₂ desorption spectra from Cu and Ni seem to desorb through the same mechanism. In the case of Pd this mechanism is controlled by adsorbed sulphur.     

Fragmentation of gold projectiles: From evaporation to total disassembly

We have studied the fragmentation of Au projectiles interacting with targets of C, Al and Cu at an incident energy ofE/A=600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with chargeZ≧2. The recorded fragmentation events were sorted according to three observables, the multiplicityM _lp of light charged particles, the largest atomic numberZ _max within an event, and a new observable,Z _bound, representing the sum of the atomic numbersZ of all fragments withZ≧2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for theC target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity andZ _bound, extending from evaporation type processes (largeZ _bound) to the total disassembly of the projectile (smallZ _bound), is independent of the target nucleus. This universal behaviour may suggest an — at least partial — equilibration of the projectile fragment prior to its decay.     

Hydrogen control of ferromagnetism in a dilute magnetic semiconductor

We show that upon exposure to a remote dc hydrogen plasma, the magnetic and electronic properties of the dilute magnetic semiconductor Ga1-xMnxAs change qualitatively. While the as-grown Ga1-xMnxAs thin films are ferromagnetic at temperatures T less, similar 70 K, the samples are found to be paramagnetic after the hydrogenation, with a Brillouin-type magnetization curve even at T=2 K. Comparing magnetization and electronic transport measurements, we conclude that the density of free holes p is significantly reduced by the plasma process, while the density of Mn magnetic moments does not change.     

Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime

Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated.