Schmidt-Bocking H.,Goethe University Frankfurt |
Schmidt L.,Goethe University Frankfurt |
Ludde H.J.,Goethe University Frankfurt |
Trageser W.,Goethe University Frankfurt |
And 2 more authors.
European Physical Journal H | Year: 2016
The Stern-Gerlach-Experiment (SGE) performed in 1922 is a seminal benchmark experiment ofquantum physics providing evidence for several fundamental properties of quantum systems.Based on the knowledge of today we illustrate the different benchmark results of the SGEfor the development of modern quantum physics and chemistry. The SGE provided the firstdirect experimental evidence for angular momentum quantization in the quantum world andtherefore also for the existence of directional quantization of all angular momenta in theprocess of measurement. Furthermore, it measured for the first time a ground stateproperty of an atom, it produced for the first time a fully “spin-polarized” atomic beam,and it also revealed the electron spin, even though this was not realized at the time. TheSGE was the first fully successful molecular beam experiment where the kinematics ofparticles can be determined with high momentum-resolution by beam measurements in vacuum.This technique provided a kind of new kinematic microscope with which inner atomic ornuclear properties could be investigated. Historical facts of the original SGE aredescribed together with early attempts by Einstein, Ehrenfest, Heisenberg, and others toreveal the physical processes creating directional quantization in the SGE. Heisenberg’sand Einstein’s proposals of an improved multi-stage SGE are presented. The firstrealization of these proposed experiments by Stern, Phipps, Frisch and Segrè is described.The experimental set-up suggested by Einstein can be considered as an anticipation of aRabi-apparatus with varying fields. Recent theoretical work by Wennerström and Westlund,by Devereux and others, is mentioned in which the directional quantization process andpossible interference effects of the two different spin states are investigated. In fullagreement with the results of the new quantum theory directional quantization appears as ageneral and universal feature of quantum measurements. One experimental example for suchdirectional quantization in scattering processes is shown. Last not least, the earlyhistory of the “almost” discovery of the electron spin in the SGE is revisited. © 2016, EDP Sciences and Springer-Verlag Berlin Heidelberg.
Frank D.,Swiss Federal Institute of forest |
Frank D.,Oeschger Center for Climate Change Research |
Esper J.,JohannesGutenberg University |
Zorita E.,Helmholtz Center Geesthacht |
Wilson R.,University of St. Andrews
Wiley Interdisciplinary Reviews: Climate Change | Year: 2010
The high-resolution reconstruction of hemispheric-scale temperature variation over the past-millennium benchmarks recent warming against more naturally driven climate episodes, such as the Little Ice Age and the Medieval Warm Period, thereby allowing assessment of the relative efficacies of natural and anthropogenic forcing factors. Icons of past temperature variability, as featured in the Intergovernmental Panel on Climate Change (IPCC) reports over nearly two decades, have changed from a schematic sketch in 1990, to a seemingly well-solved story in 2001, to more explicit recognition of significant uncertainties in 2007. In this article, we detail the beginning of the movement to reconstruct large-scale temperatures, highlight major steps forward, and present our views on what remains to be accomplished. Despite significant efforts and progress, the spatial representation of reconstructions is limited, and the interannual and centennial variation are poorly quantified. Research priorities to reduce reconstruction uncertainties and improve future projections, include (1) increasing the role of expert assessment in selecting and incorporating the highest quality proxy data in reconstructions (2) employing reconstruction ensemble methodology, and (3) further improvements of forcing series. We suggest that much of the sensitivity in the reconstructions, a topic that has dominated scientific debates, can be traced back to the input data. It is perhaps advisable to use fewer, but expert-assessed proxy records to reduce errors in future reconstruction efforts. © 2010 John Wiley & Sons, Ltd.
Medjanik K.,JohannesGutenberg University |
de Souza M.,Claro |
Kutnyakhov D.,JohannesGutenberg University |
Gloskovskii A.,German Electron Synchrotron |
And 7 more authors.
European Physical Journal B | Year: 2014
Core-level photoemission spectra of the Fabre salts with X = SbF6 and PF6 were taken using hard X-raysfrom PETRA III, Hamburg. In these salts TMTTF layers show a significant stack dimerizationwith a charge transfer of 1e per dimer to the anion SbF6 or PF6. At room temperature andslightly below the core-level spectra exhibit single lines, characteristic for awell-screened metallic state. At reduced temperatures progressive charge localization setsin, followed by a 2nd order phase transition into a charge-ordered ground state. In bothsalts groups of new core-level signals occur, shifted towards lower kinetic energies. Thisis indicative of a reduced transverse-conductivity across the anion layers, visible aslayer-dependent charge depletion for both samples. The surface potential was traced viashifts of core-level signals of an adsorbate. A well-defined potential could beestablished by a conducting cap layer of 5 nm aluminum which appears “transparent” due tothe large probing depth of HAXPES (8–10 nm). At the transition into the charge-orderedphase the fluorine 1s line of (TMTTF)2SbF6 shifts by 2.8 eV to higherbinding energy. This is a spectroscopic fingerprint of the loss of inversion symmetryaccompanied by a cooperative shift of the SbF6 anions towards the more positively charged TMTTFdonors. This shift does not occur for the X =PF6 compound, most likely due to smaller chargedisproportion or due to the presence of charge disorder. © 2014, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.