Algebraic spatial correlations in lattice gas automata violating detailed balance

In this paper we discuss the existence of generic long-range correlations in spatially homogeneous and stable equilibrium states of closed lattice gas automata whose stochastic collision rules violate the symmetry conditions of detailed balance and in addition satisfy local conservation laws. Such correlations occur even though the collision rules are strictly local and invariant under all symmetries of the lattice. First a phenomenological (Langevin equation) approach is discussed. Next we present a theoretical analysis on the basis of an approximate microscopic (ring kinetic) theory. This theory is used to calculate the amplitude ofr ^– tails in the spatial correlations, and the result is compared with computer simulations.     

Structural investigations on YbRh2Si2: from the atomic to the macroscopic length scale

YbRh2Si2 has advanced to a prototype material for investigating physics related to the Kondo effect. An optimization of the synthesis resulted in single crystals of extraordinary crystalline quality. At the atomic scale, we utilize scanning tunneling microscopy to study the topography of cleaved single crystals. A structural and chemical analysis was conducted by highly accurate x-ray diffraction and wavelength dispersive x-ray spectroscopy measurements. The latter indicate a homogeneity range of the YbRh2Si2 phase between approximately 40.0–40.2 at.% Rh. For our high-quality samples the number of defects found on the atomic scale (of the order of 0.3% of the visible lattice sites) is in quantitative agreement with a very small off-stoichiometry within this homogeneity range. Comparing our results for these samples allows an assignment of the structural defects observed at the cleaved surfaces to Rh occupying Si sites and, even less numerous Si in Rh sites. Such an analysis is hampered for samples of lesser quality, but there seem to be numerous empty Si-sites. Based on these observations the results of scanning tunneling spectroscopy can be analyzed in further detail and provide insight into the Kondo physics.     

On the interpretation of fluorescence anisotropy decays from probe molecules in lipid vesicle systems

Measurements of fluorescence depolarization decays are widely used to obtain information about the molecular order and rotational dynamics of fluorescent probe molecules in membrane systems. This information is obtained by least-squares fits of the experimental data to the predictions of physical models for motion. Here we present a critical review of the ways and means of the data analysis and address the question how and why totally different models such as Brownian rotational diffusion and wobble-in-cone provide such convincing fits to the fluorescence anistropy decay curves. We show that while these models are useful for investigating the general trends in the behavior of the probe molecules, they fail to describe the underlying motional processes. We propose to remedy this situation with a model in which the probe molecules undergo fast, though restricted local motions within a slowly rotating cage in the lipid bilayer structure. The cage may be envisaged as a free volume cavity between the lipid molecules, so that its position and orientation change with the internal conformational motions of the lipid chains. This approach may be considered to be a synthesis of the wobble-in-cone and Brownian rotational diffusion models. Importantly, this compound motion model appears to provide a consistent picture of fluorescent probe behavior in both oriented lipid bilayers and lipid vesicle systems.     

Diffusion in Lorentz lattice gas automata with backscattering

The probability of first return to the initial intervalx and the diffusion tensorD _x are calculated exactly for a ballistic Lorentz gas on a Bethe lattice or Cayley tree. It consists of a moving particle and a fixed array of scatterers, located at the nodes, and the lengths of the intervals between scatterers are determined by a geometric distribution. The same values forx andD _x apply also to a regular space lattice with a fraction of sites occupied by a scatterer in the limit of a small concentration of scatterers. If backscattering occurs, the results are very different from the Boltzmann approximation. The theory is applied to different types of lattices and different types of scatterers having rotational or mirror symmetries.     

Transportation of megawatt millijoule laser pulses via optical fibers?

Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E _p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated.     

Experimental investigation of the two-photon widths of the chi(c0) and the chi(c2) mesons

Using 12.7 fb(-1) of data collected with the CLEO detector at CESR, we observed two-photon production of the cc states chi(c0) and chi(c2) in their decay to pi(+)pi(-)pi(+)pi(-). We measured gamma(gammagamma)(chi(c))xB(chi(c)-->pi(+)pi(-)pi(+)pi(-)) to be 75+/-13(stat)+/-8(syst) eV for the chi(c0) and 6.4+/-1.8(stat)+/-0.8(syst) eV for the chi(c2), implying gamma(gammagamma)(chi(c0)) = 3.76+/-0.65(stat)+/-0.41(syst)+/-1.69(br) keV and gamma(gammagamma)(chi(c2)) = 0.53+/-0.15(stat)+/-0.06(syst)+/-0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of gamma(gammagamma)(chi(c0))/gamma(gammagamma)(chi(c2)), evaluated to be 7.4+/-2.4(stat)+/-0.5(syst)+/-0.9(br), with QCD-based predictions.     

New measurements of Cabibbo-suppressed decays of mesons with the CLEO-c detector

Using of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: pi+ pi- pi0 pi0, pi+ pi+ pi- pi- pi0, pi+ pi0 pi0, pi+ pi+ pi- pi0, eta pi0, and omega pi+ pi-. Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D --> pi pi rates allow us to extract the ratio of isospin amplitudes A(DeltaI = (3/2) / A(DeltaI = (1/2)) = 0.420 +/- 0.014(stat) +/- 0.016(syst) and the strong phase shift of delta1 = (86.4 +/- 2.8 +/- 3.3) degrees, which is quite large and now more precisely determined.     

Beitrag zur Trennung des Urans von Thorium mittels Ionenaustausches und zur fluorimetrischen Uranbestimmung

Zusammenfassung Es wird eine Uran-Thoriumtrennung mittels des stark basischen Anionenaustauschers Amberlite IRA 400 beschrieben. Uran(VI) läßt sich von Thorium und einer Reihe anderer Kationen dadurch trennen, daß es mit 6,5n Salzsäure einen negativ geladenen Komplex bildet, der am Austauscherharz sorbiert wird, während Thorium keinen Komplex bildet und daher nicht sorbiert wird. Uran wird mit 1 n Salzsäure eluiert.Zur Bestimmung des Urans wird eine genaue und empfindliche fluorimetrische Bestimmung angewendet, die durch Einfachheit und Billigkeit der dazu verwendeten Apparate gekennzeichnet ist.Das Verhalten anderer Kationen unter den Bedingungen der Trennung wurde qualitativ studiert und die Möglichkeit der Trennung des Urans und Thoriums von den erwähnten Kationen diskutiert.Herrn Prof. Dr. L. Schmid, Wien, zum 60. Geburtstag gewidmet.Für die Gewährung eines Stipendiums zur Ausführung der vorliegenden Arbeit an eine von uns (M. P.), sei der Österreichischen Gesellschaft für Mikrochemie der beste Dank ausgesprochen.Herrn Prof. Dr. F. Hecht, der diese Arbeit ermöglichte, sei für seine stete Hilfe herzlich gedankt.     

Non‐symmetric bent‐core mesogens with one terminal vinyl group

Two series of non‐symmetric banana‐shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3‐phenylene bis(4‐benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X‐ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC₈H₁₇ to OC₁₆H₃₃. The other terminal tails are OC₁₁H₂₃, O(CH₂)₉CH?=?CH₂, OC₁₀H₂₁ and O(CH₂)₈CH?=?CH₂. The short‐tailed compounds show monotropic or enantiotropic B₁ phases and the long‐tailed compounds the B₂ phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B₂ phases have layer spacings that suggest a tilt of ～45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric.