Search Results - (Author, Cooperation:D. Neumann)

2018-05-05

Institute of Physics (IOP)

1367-2630

Physics

2015-08-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Arabidopsis/*metabolism/*parasitology ; Arabidopsis Proteins/*classification/genetics/metabolism ; *Biological Evolution ; Gene Dosage ; Germination ; Heterocyclic Compounds, 1-Ring/*metabolism ; Host-Parasite Interactions ; Hydrolases/*classification/genetics/metabolism ; Lactones/*metabolism ; Orobanchaceae/*enzymology/genetics/growth & development ; Phylogeny ; Plant Growth Regulators/*metabolism ; Plant Roots/metabolism/parasitology ; Plants, Genetically Modified/genetics/metabolism

2013-06-15

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

AMP-Activated Protein Kinases/*chemistry/*metabolism ; Adenosine Diphosphate/*metabolism/*pharmacology ; Animals

2018-05-15

The American Society for Microbiology (ASM)

0022-538X

1098-5514

Medicine

2018-03-29

The American Society for Microbiology (ASM)

0022-538X

1098-5514

Medicine

1089-7550

AIP Digital Archive

Physics

Bi2Sr2MnOy, isomorphic to the high-Tc compound containing Cu, exhibits a displacement modulation driven by the bending of Bi double layers, thus creating a modulated environment for the magnetic MnO2 layers which are 12 A(ring) apart. Neutron scattering results will be presented, showing antiferromagnetic order in zero field and a field-induced transition to weak ferromagnetism. This behavior is a direct consequence of the structural modulation which breaks the symmetry of two otherwise equivalent ordering directions of (010) and (100)−the latter being associated with weak ferromagnetism. Magnetic scattering has been observed at superlattice positions, suggesting that the displacement modulation affects the valence of the magnetic ions. Subtle differences in magnetic behavior are observed in similar compounds where Pb is substituted for Bi and Ca for Sr. These results will be discussed in terms of a modulated magnetic model.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Well-defined librational excitations have been observed at energies of 2–3 meV in the low temperature ordered phase of solid C60. These relatively high energies imply a stiff orientational potential below the transition. The sharpness of the peaks indicates that this potential does not depend strongly on the axis of the angular displacement. The modes soften and broaden as the temperature approaches that of the orientational melting transition which occurs when the librational amplitude is a considerable fraction of nearest-neighbor interatomic angles.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Neutron scattering has been used to study the basal spacing and vibrational excitations of oriented samples of (CH3)3NH+ –vermiculite and its deuterated form (CD3)3ND+ –vermiculite. Both forms exhibit a basal spacing of 12.71 A(ring) and a rich vibrational spectrum in the energy range 20–140 meV for Q perpendicular and parallel to the c-axis. These results are compared with infrared measurements and inelastic neutron scattering results of trimethylammonium halides over the same energy range. The torsional mode of the methyl group has been found to be split by ∼8 meV due to the top–top interaction between the methyl groups in the trimethylammonium vermiculite.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report on an x-ray diffraction study of GaAs/GaAs1−xSbx superlattices grown by molecular-beam epitaxy on miscut GaAs (100) substrates. The fundamental reflections of the superlattice lie on a reciprocal lattice rod which is tilted with respect to the reciprocal lattice rod of the substrate. The satellite reflection, in turn, lies on lines making a constant angle with the reciprocal lattice rod containing the fundamental reflections. This result is attributed to a terraced superlattice which, in addition, is tilted with respect to the substrate. We describe a model which approximates the misfit strain imposed on the superlattice at the interfacial step, and which is capable of relating the average tilt angle to the misfit strain. The same model can also explain the transverse broadenings observed for the superlattice peaks.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A detailed x-ray scattering study of GaAs grown by molecular beam epitaxy on (001) oriented Si and Ge substrates is reported. It is shown that the broadening of the GaAs Bragg peaks can be understood in terms of residual strains for samples 2 μm thick. For a sample 0.2 μm thick, domain size broadening effects corresponding to the total thickness of the GaAs film must also be included in order to explain the peak widths. In none of the samples was any evidence of antiphase domain broadening observed and we are thus able to place a minimum of 4000 A(ring) on the size of any possible antiphase domains. We also find that the GaAs lattice is incommensurate with the Si substrate and that the GaAs is tetragonally distorted at room temperature. This distortion is explained by the difference in the thermal expansion of GaAs and Si.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report an investigation of the materials properties of GaAs on Si epitaxial layers. By using properly oriented substrates, we have found that a substantial reduction in the density of threading dislocations can be achieved. In the presence of steps, dislocations with their Burgers vectors in the (100) substrate plane are preferentially generated, which are more effective in accommodating lattice mismatch and do not thread into the epitaxial layer. We have also found that the density of threading dislocations can be reduced significantly by the use of GaAs/InGaAs pseudomorphic superlattices. Using these techniques, dislocation densities of as low as 103–104 cm−2 have been achieved in 2-μm-thick GaAs on Si epitaxial layers. In growth on nominal (100) orientations, where it is known that single atomic steps dominate, we have found no evidence of antiphase domains by transmission electron microscopy or chemical etching. This result suggests that it may not be energetically favorable for antiphase domains to form in these samples. Alternatively antiphase domains may propagate along the {111} directions and annihilate one another. For GaAs/(Al,Ga)As double heterojunction (DH) laser structures on Si substrates, the dislocation control techniques have made possible electroluminescence intensity (spontaneous emission) within a factor of 2 of state-of-the-art DH lasers on GaAs (which for reference lased at a current threshold density of 600 A/cm2). These results compare to within experimental determination. Electroluminescence intensities were also found to increase with increasing initial growth temperature. Stripe geometry lasers with room-temperature pulsed threshold currents as low as 170 mA for 10×240 μm2 stripe have been obtained using these techniques.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A method was developed for fabricating nanocrystalline microstructures. This method involves synthesizing nanoparticles in a thermal plasma expanded through a nozzle, and then focusing the nanoparticles to a collimated beam by means of aerodynamic lenses. High-aspect-ratio structures of silicon carbide and titanium were deposited on stationary substrates, and lines and two-dimensional patterns were deposited on translated substrates. Linewidths equalled approximately 50 μm. This approach allows the use of much larger nozzles than in previously developed micronozzle methods, and also allows size selection of the particles that are deposited. © 2000 American Institute of Physics.

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Neutron powder diffraction has been used to obtain the thermal parameters for the deuterium atoms and to confirm the crystal structure of acetonitrile-d3 at 4 K. Inelastic neutron scattering from both isotopic species is used to determine the energies of the first and second rotational levels of the methyl group. These four levels are reasonably reproduced by a threefold potential with V3=125 meV. The activation energy derived from this potential is in agreement with that previously obtained from the temperature dependence of T1 in proton magnetic resonance measurements.

Electronic Resource

1095-8649

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Although the total migratory activity of fishes from floodplain lakes in the Lower Rhine (Germany) into the connected drainage channels, estimated using electrofishing, fyke nets and visual observations, was low during summer 1997, conspicuous diel migrations of adult bream Abramis brama in June and July were recorded in one of the channels studied. A considerable proportion of the population of the floodplain lake immigrated into the channel at dusk and left it at dawn. During two winters (1994–1995, 1997–1998) the abundance of fishes increased considerably in the channels. The winter migrations, studied in detail in one of the channels in 1997–1998, started in late October, when the water temperature dropped below 10° C. In contrast to the mean of 500 fishes per 100 m channel length between May and October, 〉5000 fishes were found from November to March, with maximum values of 〉50 000 fishes per 100 m channel length in February 1998. More than 90% of these shoals were 0+ year fishes, dominated by roach Rutilus rutilus, bream, perch Perca fluviatilis and rudd Scardinius erythrophthalmus. These shoals entered the channel at sunrise and left it around sunset. Generally, the 0+ year fishes in the shoals swam separately from the older fishes, and different reactions towards the attack of predatory fishes were observed. The migrating shoals of juvenile fishes during the winter were interpreted as a strategy to minimize predation risk.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The abundance of metals in the hot, gaseous X-ray haloes of galaxy clusters depends crucially on the evolution of the constituent galaxies and their associated stellar populations. The metal abundances in X-ray clusters at high redshifts should therefore provide important insights into the ...

Electronic Resource

0020-1693

Azauracil complexes ; NMR spectroscopy ; Palladium complexes ; Uracil complexes

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Chemistry and Pharmacology

Electronic Resource

0014-5793

Acetylcholine receptor ; Experimental autoimmune myasthenia gravis ; mRNA

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0014-4827

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Medicine

Electronic Resource