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71.
We study the hypergraph H(P) whose vertices are the points of a finite poset and whose edges are the maximal intervals in P (i.e. sets of the form I = {{v ε P: p ν q}}, p minimal, q maximal). We mention resp. show that the problems of the determination of the independence number , the point covering number τ, the matching number v and the edge covering number p are NP-complete. For interval orders we describe polynomial algorithms and prove the König property (v = τ) and the dual König property (a = p). Finally we show that the (dual) König property is preserved by product. 相似文献
72.
73.
R. Grieser P. Merz G. Huber V. Sebastian P. Seelig M. Grieser R. Grimm I. Lauer V. Luger H.J. Miesner D. Schwalm A. Dax T. Engel M. Gerlach T. Kühl H. Winter 《Hyperfine Interactions》1997,108(1-3):241-250
Heavy ion storage rings allow for tests of the structure of local space time via the Doppler effect. At the TSR/Heidelberg
an experiment with high resolution laser spectroscopy at 7Li+ is performed. To gain the maximum resolution for saturation spectroscopy new methods of relativistic ion beam preparation
and diagnostics have been developed.
The laser cooling of the beam allows for precision determination of the mean velocity of the ions. A novel phase synchronous
detection scheme, ultimately sensitive to single ions, gives insights into the cooling mechanism and dynamics. With an additional
synchronous excitation scheme systematic uncertainties of the test experiment can be drastically reduced. After separation
of the ground state ions from the triplet states of 7Li+ by the combination of laser and electron cooling, a bunched and cooled ensemble of fast moving high precision clocks with
minimized perturbations by space charge effects and intra beam scattering is available.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
74.
W. Engel N. Eisenreich M. Herrmann V. Kolarik 《Journal of Thermal Analysis and Calorimetry》1997,49(2):1025-1037
Time and temperature resolved X-ray diffraction was used for thermal analysis. Series of diffraction patterns were measured, while the samples are heated/cooled stepwise or isothermally with freely selectable temperature programs.The method was applied for the investigation of the phase transitions of ammonium nitrate and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane), when the identification of phases was required. Its capability in the field of kinetics is demonstrated with the isothermal investigation of the solid state reaction of ammonium nitrate with copper oxide and the non-isothermal investigation of the high temperature corrosion of nickel, which was performed by means of a difference procedure. For obtaining structural details peak fitting and Rietveld refinement were applied for the investigation of ammonium nitrate and HMX.We are indebted to Mr. K. O. Hartmann, Mr. H. Fietzek and Mr. H. G. Farr for their assistance during the measurements and for the maintenance of the measuring systems. 相似文献
75.
76.
Two-dimensional electronic spectroscopy (2D ES) maps the electronic structure of complex systems on a femtosecond time scale. While analogous to multidimensional NMR spectroscopy, 2D optical spectroscopy differs significantly in its implementation. Yet, 2D Fourier spectroscopies still require point-by-point sampling of the time delay between two pulses responsible for creating quantum coherence among states. Unlike NMR, achieving the requisite phase stability at optical frequencies between these pulse pairs remains experimentally challenging. Nonetheless, 2D optical spectroscopy has been successfully demonstrated by combining passive and active phase stabilization along with precise control of optical delays and long-term temperature stability, although the widespread adoption of 2D ES has been significantly hampered by these technical challenges. Here, we exploit an analogy to magnetic resonance imaging (MRI) to demonstrate a single-shot method capable of acquiring the entire 2D spectrum in a single laser shot using only conventional optics. Unlike point-by-point sampling protocols typically used to record 2D spectra, this method, which we call GRadient-Assisted Photon Echo (GRAPE) spectroscopy, largely eliminates phase errors while reducing the acquisition time by orders of magnitude. By incorporating a spatiotemporal encoding of the nonlinear polarization along the excitation frequency axis of the 2D spectrum, GRAPE spectroscopy achieves no loss in signal while simultaneously reducing overall noise. Here, we describe the principles of GRAPE spectroscopy and discuss associated experimental considerations. 相似文献
77.
Gregory S. Engel 《Procedia Chemistry》2011,3(1):222-231
Quantum coherence improves the quantum efficiency of excitonic energy transport within the Fenna-Matthews-Olson photosynthetic complex from the green sulphur bacterium, Chlorobium tepidum. Experimental evidence from third-order nonlinear spectroscopies provides clear evidence of quantum coherence among excited states persisting for picoseconds despite rapid (<100fs) dephasing of quantum coherence between ground and excited states. This protection of quantum coherence can arise from multiple mechanisms, but the net effect is the same: the energetic landscape is course-grained thereby improving efficiency by effectively smoothing the rugged energetic landscape while simultaneously eliminating trap states. The protein bath enables the unusual observed dynamics and illustrates some simple design principles that provide direction to synthetic efforts to mimic the effect. This communication provides an overview of experimental and theoretical notions for those interested in exploiting design principles of photosynthetic energy transfer in synthetic systems. 相似文献
78.
AR Engel 《Contemporary Physics》2013,54(6):523-526
This article reviews some of the applications of physics to the solution of archaeological problems. The use of magnetic, resistivity and electromagnetic surveying techniques for the location of buried features is described. Various methods of age determination are outlined while the problems associated with radiocarbon dating of organic material and thermoluminescent dating of pottery are discussed in detail. The techniques, including petrological examination, chemical analysis and isotopic analysis, employed in the physical examination of archaeological artefacts are described. Examples of the application of these techniques in establishing the source of the raw materials used in pottery, metal and stone implements and in elucidating the techniques of manufacture of pottery and metal objects are also given. 相似文献
79.
R. Engel 《Fresenius' Journal of Analytical Chemistry》1876,15(1):344
Ohne Zusammenfassung 相似文献
80.