476 research outputs found
Measuring a diffusion coefficient by single-particle tracking : statistical analysis of experimental mean squared displacement curves
How the number of fitting points for the slope of the mean-square displacement influences the experimentally determined particle size distribution from single-particle tracking
Tuning the structural instability of SrTiO_3 by Eu doping: The phase diagram of Sr_1-xEu_xTiO_3
The phase diagram of Sr_1-xEu_xTiO_3 is determined experimentally by electron
paramagnetic resonance and resistivity measurements and analyzed theoretically
within the self-consistent phonon approximation as a function of x
([0.03-1.0]). The transition temperature of the structural instability of the
system increases nonlinearly to higher temperatures with increasing x. This is
interpreted theoretically by a substantial alteration in the dynamics caused by
a change in the double-well potential from broad and shallow to narrow and
deep.Comment: 15 pages, 5 figure
Electronic Structure and Lattice dynamics of NaFeAs
The similarity of the electronic structures of NaFeAs and other Fe pnictides
has been demonstrated on the basis of first-principle calculations. The global
double-degeneracy of electronic bands along X-M and R-A direction indicates the
instability of Fe pnictides and is explained on the basis of a tight-binding
model. The de Haas-van Alphen parameters for the Fermi surface (FS) of NaFeAs
have been calculated. A spin density wave (SDW)
instead of a charge density wave (CDW) ground state is predicted based on the
calculated generalized susceptibility and a criterion
derived from a restricted Hatree-Fock model. The strongest electron-phonon
(e-p) coupling has been found to involve only As, Na z-direction vibration with
linear-response calculations. A possible enhancement mechanism for e-p coupling
due to correlation is suggested
Experimental Comparison of the Refrigerant Reservoir Position in a Primary Loop Refrigerant Cycle with Optimal Operation
Recent attempts to find energy-efficient thermal management systems for electric and plug-in hybrid electric vehicles have led to secondary loop systems as an alternative approach to meet dynamic heating and cooling demands and reduce refrigerant charge. As such, a thorough understanding of the vapor compression cycle, which serves as the central thermal supply unit, is required. In addition to design considerations concerning the type and size of components such as the heat exchangers or compressor, the refrigerant reservoir choice between a high pressure receiver or a low pressure accumulator is critical for energy-efficient operation under varying operation conditions. In this work, two possible positions of the accumulator/receiver are experimentally examined and optimal control is applied. Therefore, either the superheating at the compressor inlet or outlet of the receiver system or the subcooling at the condenser outlet of the accumulator system are chosen as control variables and adjusted by an electrical expansion valve. Experimental results based on a simple automotive R134a primary loop system containing a scroll compressor are presented. Comparing these two different systems with a receiver or an accumulator, a receiver system shows a slightly higher COP under the examined operation conditions when operated optimally. However the receiver/accumulator position has a non-negligible impact on high and low pressure itself resulting in an advantage for the accumulator system in a cold winter scenario
Limitations of Linear Dichroism Spectroscopy for Elucidating Structural Issues of Light-Harvesting Aggregates in Chlorosomes
Linear dichroism (LD) spectroscopy is a widely used technique for studying the mutual orientation of the transition-dipole moments of the electronically excited states of molecular aggregates. Often the method is applied to aggregates where detailed information about the geometrical arrangement of the monomers is lacking. However, for complex molecular assemblies where the monomers are assembled hierarchically in tiers of supramolecular structural elements, the method cannot extract well-founded information about the monomer arrangement. Here we discuss this difficulty on the example of chlorosomes, which are the light-harvesting aggregates of photosynthetic green-(non) sulfur bacteria. Chlorosomes consist of hundreds of thousands of bacteriochlorophyll molecules that self-assemble into secondary structural elements of curved lamellar or cylindrical morphology. We exploit data from polarization-resolved fluorescence-excitation spectroscopy performed on single chlorosomes for reconstructing the corresponding LD spectra. This reveals that LD spectroscopy is not suited for benchmarking structural models in particular for complex hierarchically organized molecular supramolecular assemblies
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