On the crystal structure and magnetic properties of MnNiGe

MnNiGe has been studied by X-ray and neutron diffraction to elucidate its structural and magnetic properties. The structure at room temperature is of the orthorhombic TiNiSi type, but transforms on heating above 528 K to the hexagonal ordered Ni₂In type. Below 356 K a spiral magnetic structure with propagation vector τ = 0.228 × 2πa^* is found. At 260 K an abrupt change in the intensity of the satellite reflections with no change in the propagation vector is attributed to the formation of a double spiral structure. Discrepancies between these findings and the results of previous measurements are attributed to differences in sample preparation.     

Camera orientation and 3D-deformation measurement by use of cross gratings

The orientation of stereo cameras in a close range environment is derived by a modified bundle block adjustment, using the cross coordinates of a shifted high quality grating. By means of the HOUGH-transform, approximate grating coordinates are determined, which are used to calculate the final coordinates fully automatically with a correlation filter technique. The stereo setup is applied to measure the 3D-deformation on the surface of a cold welded Cu---Al tension specimen supplied with a titanium dioxide cross grating.     

Single-pulse collision-insensitive picosecond planar laser-induced fluorescence of OHA 2 Σ + (v′ = 2) in atmospheric-pressure flames

Single-pulse two-dimensional picosecond Laser-Induced Fluorescence (LIF) imaging of the OH density in a single quantum state was performed for the first time, using a premixed methane-oxygen flame at atmospheric pressure. A picosecond, excimer-Raman-laser system (268 nm, 470 ps FWHM) was used for excitation of OH. The fluorescence from the laser sheet was imaged onto a fast gated intensified camera with a 400 ps gate width. The short laser pulse minimizes the collisional redistribution of population in the ground state during excitation, while the short camera gate avoids significant quenching of the excited-state fluorescence. The fluorescence signal obtained in this way is a direct measure of the population in a selected quantum state. In contrast to common nanosecond LIF signals no corrections on variations of the collisional environment are necessary. This collision-insensitive approach to two-dimensional LIF yields an OH detection limit of 10 ppm in a cube of 330 µm per side with a single 1 mJ laser pulse. A rate-equation model is used to estimate the effects on the observed signal of fluctuations in pulse energy and duration, laser-camera timing jitter, and spatial variations in the collisional environment.     

Synthesis of anti-tumour phosphatidylinositol analogues from glucose by the use of ring-closing olefin metathesis

A divergent strategy is described for synthesis of the novel phosphatidylinositols 1-3. The synthetic approach commences from benzyl-protected methyl 6-iodo-6-deoxy-alpha-D-glucopyranoside, which undergoes zinc-mediated reductive fragmentation followed by vinyl Grignard addition and ring-closing metathesis to afford the key conduritol B intermediate 7. This can trifurcate to form three different benzyl-protected myo-inositol headgroups 4-6, which after phosphorylation and attachment of the glycerolipid part give phosphatidylinositols 1-3. Preliminary biological testing against human colon adenocarcinoma cells reveals that analogues 1-3 are significant anti-tumour agents.     

Proteolytic cleavage reveals interaction patterns between silica nanoparticles and two variants of human carbonic anhydrase

To characterize the sites on the protein surface that are involved in the adsorption to silica nanoparticles and the subsequent rearrangements of the protein/nanoparticle interaction, a novel approach has been used. After incubation of protein with silica nanoparticles for 2 or 16 h, the protein was cleaved with trypsin and the peptide fragments were analyzed with mass spectrometry. The nanoparticle surface area was in 16-fold excess over available protein surface to minimize the probability that the initial binding would be affected by other protein molecules. When the fragment patterns obtained in the presence and absence of silica nanoparticles were compared, we were able to characterize the protein fragments that interact with the surface. This approach has allowed us to identify the initial binding sites on the protein structure and the rearrangement of the binding sites that occur upon prolonged incubation with the surface.     

Hydrogen maser frequency shifts due to coherently excited Δm F =±1 transitions betweenF=1 levels of the atomic hydrogen ground state

Hydrogen maser frequency shifts, caused by the multiple quantum transition nonlinearities of a resonant multiple frequency excitation of the atomic hydrogen four level ground state system have been investigated. The oscillation characteristics of hydrogen maser operation with simultaneously excited, low frequencyΔm _F =±1 transitions between theF=1 states of the atomic hydrogen ground state have been analysed theoretically and explicit formulas for hydrogen maser frequency shifts and amplitude response have been derived for arbitrary maser oscillation amplitude and a small signal approximation for theΔm _F =±1 “Zeeman” transitions. The comparison with experimentally observed hydrogen maser frequency shifts was specialized to small magnetic fields, for which the difference between the resonance frequencies of the two low frequency,Δm _F =±1 Zeeman transitions is small compared to the linewidth. Special emphasis was placed on the evaluation of frequency pulling effects for a Zeeman transition excitation at off-resonance conditions. For this case the theoretical formulation of frequency pulling effects becomes insensitive against simplifying assumptions about the radiation damping phenomena and a particular good agreement between experiment and theory can therefore be expected. Experimental conditions have been specified, for which the uncertainty of hydrogen maser frequency due to Zeeman transition induced frequency shifts does not restrict the present frequency stability of a hydrogen maser frequency standard.     

Magnetic structure of cubic spinels MnxCr3−xO4 (x=1.0−1.6)

Neutron diffraction study on samples Mn_xCr_3?xO₄ with x=1.0, 1.2, 1.4 and 1.6 has been performed at temperatures below ～40 K where magnetic ordering is present. At 5 K the structure of the MnCr₂O₄ compound was found to be a general LKDM magnetic spiral with the propagation vector deviating by 13.3″ from the [110] axis. This results differs from previous findings. At about 16 K the structure becomes collinear. In samples higher content of manganese the magnetic structure is collinear over the whole temperature region (5–40) K, i.e. in the sense of long range ordering. However, a short range ordering of the transverse components of the spins is present both in these samples and in MnCr₂O₄ above 16 K.     

Hydrogen maser atomic beam resonances

Au^? ions at anionic places are formed in gold doped crystals by a reducing treatment withF centers. The ultraviolet absorption consists of 4 bands, which are namedA, B, C, andD in analogy to the isoelectronic centers of the s² type, like Tl⁺. TheB band oszillator strength strongly increases with temperature in accordance with a phonon allowed transition. The ratio of the dipole strength of theC band to that of theA band as a function of the relative position of theB band is compared with Suganos prediction. Zero phonon lines are found at helium temperatures for theA band in NaCl (2,985 Å), KCl (3,068 Å), and KBr (3,145 Å) and for theC band in KCl (2,329 Å). In KCl the Huang-Rhys factor isg=3.4 for theA band. The vibronic structure comes from the relatively large radius 6s ² state of the negative ion. Uniaxial stress splits the zero phonon line. The results definitely agree with the stress splitting behaviour of a degenerateΓ ₁→Γ ₄ transition. Inversion symmetry of the center is confirmed by the absence of a linear Stark effect.