1,487 research outputs found
Magnetic properties of a capped kagome molecule with 60 quantum spins
We compute ground-state properties of the isotropic, antiferromagnetic
Heisenberg model on the sodalite cage geometry. This is a 60-spin spherical
molecule with 24 vertex-sharing tetrahedra which can be regarded as a molecular
analogue of a capped kagome lattice and which has been synthesized with
high-spin rare-earth atoms. Here, we focus on the case where quantum
effects are strongest. We employ the SU(2)-symmetric density-matrix
renormalization group (DMRG).
We find a threefold degenerate ground state that breaks the spatial symmetry
and that splits up the molecule into three large parts which are almost
decoupled from each other. This stands in sharp contrast to the behaviour of
most known spherical molecules. On a methodological level, the disconnection
leads to "glassy dynamics" within the DMRG that cannot be targeted via standard
techniques.
In the presence of finite magnetic fields, we find broad magnetization
plateaus at 4/5, 3/5, and 1/5 of the saturation, which one can understand in
terms of localized magnons, singlets, and doublets which are again nearly
decoupled from each other. At the saturation field, the zero-point entropy is
in units of the Boltzmann constant
Surface Display of Complex Enzymes by in Situ SpyCatcher-SpyTag Interaction
The display of complex proteins on the surface of cells is of great importance for protein engineering and other fields of biotechnology. Herein, we describe a modular approach, in which the membrane anchor protein Lpp-OmpA and a protein of interest (passenger) are expressed independently as genetically fused SpyCatcher and SpyTag units and assembled in situ by post-translational coupling. Using fluorescent proteins, we first demonstrate that this strategy allows the construct to be installed on the surface of E. coli cells. The scope of our approach was then demonstrated by using three different functional enzymes, the stereoselective ketoreductase Gre2p, the homotetrameric glucose 1-dehydrogenase GDH, and the bulky heme- and diflavin-containing cytochrome P450 BM3 (BM3). In all cases, the SpyCatcher-SpyTag method enabled the generation of functional whole-cell biocatalysts, even for the bulky BM3, which could not be displayed by conventional fusion with Lpp-OmpA. Furthermore, by using a GDH variant carrying an internal SpyTag, the system could be used to display an enzyme with unmodified N- and C-termini
Performance of the EUDET-type beam telescopes
Test beam measurements at the test beam facilities of DESY have been
conducted to characterise the performance of the EUDET-type beam telescopes
originally developed within the EUDET project. The beam telescopes are equipped
with six sensor planes using MIMOSA26 monolithic active pixel devices. A
programmable Trigger Logic Unit provides trigger logic and time stamp
information on particle passage. Both data acquisition framework and offline
reconstruction software packages are available. User devices are easily
integrable into the data acquisition framework via predefined interfaces.
The biased residual distribution is studied as a function of the beam energy,
plane spacing and sensor threshold. Its standard deviation at the two centre
pixel planes using all six planes for tracking in a 6\,GeV
electron/positron-beam is measured to be
(2.88\,\pm\,0.08)\,\upmu\meter.Iterative track fits using the formalism of
General Broken Lines are performed to estimate the intrinsic resolution of the
individual pixel planes. The mean intrinsic resolution over the six sensors
used is found to be (3.24\,\pm\,0.09)\,\upmu\meter.With a 5\,GeV
electron/positron beam, the track resolution halfway between the two inner
pixel planes using an equidistant plane spacing of 20\,mm is estimated to
(1.83\,\pm\,0.03)\,\upmu\meter assuming the measured intrinsic resolution.
Towards lower beam energies the track resolution deteriorates due to increasing
multiple scattering. Threshold studies show an optimal working point of the
MIMOSA26 sensors at a sensor threshold of between five and six times their RMS
noise. Measurements at different plane spacings are used to calibrate the
amount of multiple scattering in the material traversed and allow for
corrections to the predicted angular scattering for electron beams
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