1,037 research outputs found
Chemical and photochemical oxygenation of a phytochrome Pr chromophore model pigment to purpurins
Localization of RNA polymerase I in interphase cells and mitotic chromosomes by light and electron microscopic immunocytochemistry.
Chemical Bonding and Charge Distribution at Metallic Nanocontacts
We present results of electronic structure calculations for aluminium
contacts of atomic size, based on density functional theory and the local
density approximation. Addressing the atomic orbitals at the neck of the
nanocontact, we find that the local band structure deviates strongly from bulk
fcc aluminium. In particular, hybridization between Al 3s and 3p states is
fully suppressed due to directed bonds at the contact. Moreover, a charge
transfer of 0.6 electrons off the contact aluminium site is found. Both the
suppressed hybridization and the violated charge neutrality are characteristic
features of metallic nanocontacts. This fact has serious consequences for
models aiming at a microscopic description of transport properties.Comment: 6 pages, 3 figures, accepted by Chemical Physics Letter
Spectral diffusion and 14N quadrupole splittings in absorption detected magnetic resonance hole burning spectra of photosynthetic reaction centers
Zero field absorption detected magnetic resonance hole burning measurements were performed on photosynthetic reaction centers of the bacteria Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis. Extrapolation to zero microwave power yielded pseudohomogeneous linewidths of 2.0 MHz for Rhodopseudomonas viridis, 1.0 and 0.9 MHz for the protonated forms of Rhodobacter sphaeroides R26 with and without monomer bacteriochlorophyll exchanged, and 0.25 MHz as an upper limit for fully deuterated reaction centers of Rhodobacter sphaeroides R26. The measured linewidths were interpreted as being due to unresolved hyperfine interaction between the nuclear spins and the triplet electron spin, the line shape being determined by spectral diffusion among the nuclei. The difference in linewidths between Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis is then explained by triplet delocalization on the special pair in the former, and localization on one dimer half on the latter. In the fully deuterated sample, four quadrupole satellites were observed in the hole spectra arising from the eight 14N nitrogens in the special pair. The quadrupole parameters seem to be very similar for all nitrogens and were determined to =1.25±0.1 MHz and =0.9±0.1 MHz. The Journal of Chemical Physics is copyrighted by The American Institute of Physics
Geometry Effects at Atomic-Size Aluminium Contacts
We present electronic structure calculations for aluminium nanocontacts.
Addressing the neck of the contact, we compare characteristic geometries to
investigate the effects of the local aluminium coordination on the electronic
states. We find that the Al 3pz states are very sensitive against modifications
of the orbital overlap, which has serious consequences for the transport
properties. Stretching of the contact shifts states towards the Fermi energy,
leaving the system instable against ferromagnetic ordering. By spacial
restriction, hybridization is locally suppressed at nanocontacts and the charge
neutrality is violated. We discuss the influence of mechanical stress by means
of quantitative results for the charge transfer.Comment: 10 pages, 4 figures, accepted by Chem. Phys. Let
Interactive Image Guided Surgical Navigation - A First Step Towards Minimally Invasive Orthopaedic Surgery
Quantum Conductance in Semimetallic Bismuth Nanocontacts
Electronic transport properties of bismuth nanocontacts are analyzed by means
of a low temperature scanning tunneling microscope. The subquantum steps
observed in the conductance versus elongation curves give evidence of atomic
rearrangements in the contact. The underlying quantum nature of the conductance
reveals itself through peaks in the conductance histograms. The shape of the
conductance curves at 77 K is well described by a simple gliding mechanism for
the contact evolution during elongation. The strikingly different behaviour at
4 K suggests a charge carrier transition from light to heavy ones as the
contact cross section becomes sufficiently small.Comment: 5 pages including 4 figures. Accepted for publication in Phys. Rev.
Let
Probing the shape of atoms in real space
The structure of single atoms in real space is investigated by scanning
tunneling microscopy. Very high resolution is possible by a dramatic reduction
of the tip-sample distance. The instabilities which are normally encountered
when using small tip-sample distances are avoided by oscillating the tip of the
scanning tunneling microscope vertically with respect to the sample. The
surface atoms of Si(111)-(7 x 7) with their well-known electronic configuration
are used to image individual samarium, cobalt, iron and silicon atoms. The
resulting images resemble the charge density corresponding to 4f, 3d and 3p
atomic orbitals.Comment: Submitted to Phys. Rev. B, 17 pages, 7 figure
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