Corner spontaneous magnetization

Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet.     

Rotational temperature and density measurements in a hypersonic flow by dual-line CARS

Rotational temperature and nitrogen number density are measured in the shock wave/boundary layer interaction region in the vicinity of a two-dimensional compression corner disposed in a low pressure, 55 K, Mach 10 hypersonic air flow. Spatially-resolved data are recorded using a nonlinear optical technique named dual-line coherent anti-Stokes Raman scattering (DLCARS). Averaged temperature and density profiles are compared with those predicted by a Navier-Stokes solver. Good agreement is found.     

Branched chain discotics Phase structure and orientation behaviour

Studies show that branching the side chains of hexakis(acoyloxy)-benzenes (HAB) and -cyclohexanes (HAChx) does not modify the structure of the discotic mesophase formed. Shear fields appear to act on entire columns, not on individual discs, thereby causing alignment of columns in the shear direction. X-ray diffraction patterns of samples at temperatures between 30°C and 40°C above the clearing temperature provide evidence for the presence of mesophase order.     

A shock tube study of the reaction of methyl radicals with hydroxyl radicals

The reaction of CH₃ with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 10¹³ cm³/mol-s was measured for removal of OH by CH₃. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH₃ at these conditions is their combination to form CH₃OH. Rate coefficients of (5.3 ± 0.8) × 10¹² and (9.0 ± 1.4) × 10¹² cm³/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure.     

Zeeman transitions in deuterium atoms induced by ultra-relativistic electrons

We present data showing hyperfine transitions in an atomic deuterium beam induced by the (476 MHz) radio-frequency field of a 704 MeV electron beam in a storage ring. A polarized deuterium beam, produced in an atomic beam source, was crossed with a stored electron beam and analyzed with a Breit--Rabi polarimeter. Electron-beam induced transitions were singled out by injecting different combinations of hyperfine states. Transition probabilities as high as 70% were measured at large currents (~ 100 mA). All possible deuterium transitions for a radio-frequency of 476 MHz were observed. In addition, a 1--6 transition resulting from the first harmonic (952 MHz) was observed. The effects of these transitions are of general importance for the polarized internal target technique applied in nuclear and particle physics experiments. The data are reasonably described by numerical estimates. The observed mechanism can be exploited to create nuclear polarized atoms when injecting electron polarized atoms with no net nuclear polarization into a storage cell. However, when nuclear polarized atoms are injected, care should be taken to avoid this mechanism, since it would result in depolarization of the atoms. The studies enabled us to choose the magnetic guide field during our spin-dependent electron--deuteron scattering experiments, such that electron-beam induced depolarizing effects were avoided. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetism in electron-doped copper oxides

We report muon spin relaxation/rotation measurements on sintered powder samples of Nd_2−x Ce _x CuO_4−y and a large single crystal of Nd₂CuO_4−y . We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La_2−x Sr _x CuO_4−y , although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins. Static magnetic order in Nd₂CuO_4−y appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of these materials.     

The liquid-crystalline behaviour of amphiphilic ethane-1,2-diol derivatives incorporating a six membered ring in their principal structure

Novel 3-phenyloxy substituted propane-1,2-diol derivatives, 4-(4-n-hexyloxyphenyl)-butane-1,2-diol and 4-(trans-4-n-pyropylcyclohexyl)-butane-1,2-diol have been synthesized and their thermal behaviour has been studied. These compounds exhibit thermotropic and, after addition of water, also lyotropic liquid-crystalline behaviour. The clearing temperatures of the smectic mesophases were found to be strongly dependent on the alkyl chain length and on the structural units that link the aromatic ring to the alkyl chain and to the diol unit. The behaviour of the aromatic compounds is compared with that of the cyclohexane derivative. Thereby it has been realized that the mesophase stability of the amphiphilic diols incorporating a rigid unit is largely determined by both, the molecular geometry (molecular shape and intramolecular flexibility) and the amphiphilic structural pattern.     

The Cern (g-2) measurements

Measurements of the anomalous magnetic moment of the muon are reviewed. The emphasis is put on the first one of a series of three CERN experiments which led to an experimental value ofa=1165922.9 (8.5)·10⁻⁹ (±7.2ppm), and which compares well with the present theoretical resulta=1165919.2 (1.8)·10⁻⁹ (±1.5ppm).     

Testing deviations from the inverse square law with a freely falling gravity gradiometer at balloon altitudes

Summary We discuss a null experiment to search for the fifth force at ranges around 10 km. It is proposed to use a three-axis gravity gradiometer to measure the trace of the Earth gravity tensor from a freely falling elevator dropped by a balloon. The main error sources are considered to some extent. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.