81 research outputs found
The Stern-Gerlach Experiment Revisited
The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment
of quantum physics providing evidence for several fundamental properties of
quantum systems. Based on today's knowledge we illustrate the different
benchmark results of the SGE for the development of modern quantum physics and
chemistry.
The SGE provided the first direct experimental evidence for angular momentum
quantization in the quantum world and thus also for the existence of
directional quantization of all angular momenta in the process of measurement.
It measured for the first time a ground state property of an atom, it produced
for the first time a `spin-polarized' atomic beam, it almost revealed the
electron spin. The SGE was the first fully successful molecular beam experiment
with high momentum-resolution by beam measurements in vacuum. This technique
provided a new kinematic microscope with which inner atomic or nuclear
properties could be investigated.
The original SGE is described together with early attempts by Einstein,
Ehrenfest, Heisenberg, and others to understand directional quantization in the
SGE. Heisenberg's and Einstein's proposals of an improved multi-stage SGE are
presented. The first realization of these proposals by Stern, Phipps, Frisch
and Segr\`e is described. The set-up suggested by Einstein can be considered an
anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which
the directional quantization process and possible interference effects of the
two different spin states are investigated.
In full agreement with the results of the new quantum theory directional
quantization appears as a general and universal feature of quantum
measurements. One experimental example for such directional quantization in
scattering processes is shown. Last not least, the early history of the
`almost' discovery of the electron spin in the SGE is revisited.Comment: 50pp, 17 fig
Monkey-based Research on Human Disease: The Implications of Genetic Differences
Assertions that the use of monkeys to investigate human diseases is valid scientifically are frequently based on a reported 90–93% genetic similarity between the species. Critical analyses of the relevance of monkey studies to human biology, however, indicate that this genetic similarity does not result in sufficient physiological similarity for monkeys to constitute good models for research, and that monkey data do not translate well to progress in clinical practice for humans. Salient examples include the failure of new drugs in clinical trials, the highly different infectivity and pathology of SIV/HIV, and poor extrapolation of research on Alzheimer’s disease, Parkinson’s disease and stroke. The major molecular differences underlying these inter-species phenotypic disparities have been revealed by comparative genomics and molecular biology — there are key differences in all aspects of gene expression and protein function, from chromosome and chromatin structure to post-translational modification. The collective effects of these differences are striking, extensive and widespread, and they show that the superficial similarity between human and monkey genetic sequences is of little benefit for biomedical research. The extrapolation of biomedical data from monkeys to humans is therefore highly unreliable, and the use of monkeys must be considered of questionable value, particularly given the breadth and potential of alternative methods of enquiry that are currently available to scientists
Ellen Clark, Toledo, Ohio [approximately 1890]
A cabinet card portrait of Ellen Clark once displayed by the Ford Post Number 14 of the Grand Army of the Republic (G.A.R.). The Ford Post was established in Toledo in 1867 as an organization for Union veterans of the American Civil War. Ms. Clark was a member of the Ford Circle, the ladies' G.A.R. division. Terms associated with the photograph are: Clark, Ellen | military decorations | Grand Army of the Republic. Ford Post No.14 (Toledo, Ohio) | United States--History--Civil War, 1861-186
New and little known marine nematodes from a Scottish sandy beach
13 spp of freeliving marine nematodes from the sandy beach at Firemore Bay, Wester-Ross, Scotland, are described. Amongst these the authors have proposed one gen.n., Gairleanema, with the type sp G /anagremilae gen et sp.n. 11 others are sp.n.referable to existing gen: Odontophora exharena sp.n., Theristus (Daptonema) gelana sp.n., Cobbia caledonia sp.n., Gonionchus inaequalis sp.n., Xyala smo sp.n., Siphonolaimus ewensis sp.n., Metachromadora (Bradylaimus) scotlandica sp.n., Microlaimus acinaces sp.n., Dasynemella albaensis sp.n., Rhabdodemania imer sp.n., and Triliptium parisetum sp.n. 1 sp (Trefusia zostericola Allgen. 1933) is redescribed, since it was hitherto poorly known
Distribution and fate of aliphatic and aromatic hydrocarbons in Antarctic fauna and environment
Freeliving marine nematodes. Part 1. British Enoplids. Synopses of the British Fauna No. 28
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