An exhibition that has yet to be

Winfried Oppelt was one of the great pioneers of German control engineering. In 1972 he made a detailed proposal for a permanent exhibition on control engineering at the Deutsches Museum, Munich. The intriguing proposal, which was never realised, included a set of detailed hand drawings by Oppelt. This paper, drawing on an earlier German publication, presents Oppelt's ideas and indicates why it was not accepted

Precision isotope shift measurements in Ca+^+ using highly sensitive detection schemes

We demonstrate an efficient high-precision optical spectroscopy technique for single trapped ions with non-closed transitions. In a double-shelving technique, the absorption of a single photon is first amplified to several phonons of a normal motional mode shared with a co-trapped cooling ion of a different species, before being further amplified to thousands of fluorescence photons emitted by the cooling ion using the standard electron shelving technique. We employ this extension of the photon recoil spectroscopy technique to perform the first high precision absolute frequency measurement of the $^{2}$D$_{3/2}$ $\rightarrow$ $^{2}$P$_{1/2}$ transition in $^{40}$Ca$^{+}$, resulting in a transition frequency of $f=346\, 000\, 234\, 867(96)$ kHz. Furthermore, we determine the isotope shift of this transition and the $^{2}$S$_{1/2}$ $\rightarrow$ $^{2}$P$_{1/2}$ transition for $^{42}$Ca$^{+}$, $^{44}$Ca$^{+}$ and $^{48}$Ca$^{+}$ ions relative to $^{40}$Ca$^{+}$ with an accuracy below 100 kHz. Improved field and mass shift constants of these transitions as well as changes in mean square nuclear charge radii are extracted from this high resolution data

Spontaneous Follicular Exclusion of SHP1-deficient B Cells Is Conditional on the Presence of Competitor Wild-type B Cells

Engagement of antigen receptors on mature B lymphocytes is known to block cell entry into lymphoid follicles and promote accumulation in T cell zones, yet the molecular basis for this change in cell distribution is not understood. Previous studies have shown that follicular exclusion requires a threshold level of antigen receptor engagement combined with occupancy of follicles by B cells without equivalent receptor engagement. The possibility has been raised that follicular composition affects B cell positioning by altering the amount of available antigen and the degree of receptor occupancy. Here we show that follicular composition affects migration of mature B cells under conditions that are independent of antigen receptor occupancy. B cells deficient in the negative regulatory protein tyrosine phosphatase, SHP1, which have elevated intracellular signaling by the B cell receptor, are shown to accumulate in the T zone in the absence of their specific antigen. Follicular exclusion of SHP1–deficient B cells was found to be conditional on the presence of excess B cells that lack elevated intracellular signaling, and was not due to a failure of SHP-1–deficient cells to mature and express the follicle-homing chemokine receptor Burkitt's lymphoma receptor 1. These findings strongly suggest that signals that are negatively regulated by SHP1 promote B cell localization in T cell zones by reducing competitiveness for follicular entry, and provide further evidence that follicular composition influences the positioning of antigen-engaged B cells

Chemical ozone loss in the Arctic winter 1991–1992

Chemical ozone loss in winter 1991–1992 is recalculated based on observations of the HALOE satellite instrument, Version 19, ER-2 aircraft measurements and balloon data. HALOE satellite observations are shown to be reliable in the lower stratosphere below 400 K, at altitudes where the measurements are most likely disturbed by the enhanced sulfate aerosol loading, as a result of the Mt.~Pinatubo eruption in June 1991. Significant chemical ozone loss (13–17 DU) is observed below 380 K from Kiruna balloon observations and HALOE satellite data between December 1991 and March 1992. For the two winters after the Mt. Pinatubo eruption, HALOE satellite observations show a stronger extent of chemical ozone loss towards lower altitudes compared to other Arctic winters between 1991 and 2003. In spite of already occurring deactivation of chlorine in March 1992, MIPAS-B and LPMA balloon observations indicate that chlorine was still activated at lower altitudes, consistent with observed chemical ozone loss occurring between February and March and April. Large chemical ozone loss of more than 70 DU in the Arctic winter 1991–1992 as calculated in earlier studies is corroborated here

Molecular mechanisms of kinetochore microtubule attachment

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.To ensure equal chromosome segregation during mitosis, the macromolecular kinetochore must remain attached to depolymerizing microtubules, which drive poleward chromosome movement. Microtubules are highly dynamic structures that undergo dramatic structural changes during depolymerization. The results presented in this thesis define essential functions of the Astrin-SKAP-LC8 and Skal complexes at the kinetochore-microtubule interface. First, we demonstrate that the Astrin-SKAP-LC8 complex localizes preferentially to kinetochores of bioriented sister chromatids. Localization of the Astrin-SKAP-LC8 complex to kinetochores is controlled by a key regulator of kinetochore-microtubule attachments, Aurora B kinase. The Astrin-SKAP-LC8 complex is essential for mitotic progression and directly associates with microtubules. Furthermore, the microtubule polymerization factor CLASP requires the Astrin-SKAP-LC8 complex to localize to kinetochores. Second, we demonstrate that the Skal complex has many of the biochemical and biophysical properties of a molecular machine that can couple microtubule depolymerization to chromosome movement. The Skal complex diffuses on and tracks with depolymerizing microtubules and its microtubule binding activity is necessary to maintain kinetochore-fibers and power chromosome oscillations during metaphase. Importantly, we demonstrate that the Skal complex directly interacts with the peeling protofilaments present at the depolymerizing microtubule end, suggesting a unique mechanism by which the Skal complex remains attached to depolymerizing microtubules. Finally, we demonstrate that the Skal microtubule-binding domain has two conserved basic regions that are required for microtubule binding and are subject to regulation by Aurora B kinase. In total, we define essential properties of the Astrin-SKAP-LC8 and Skal complex required for the formation of kinetochore microtubule attachments.by Jens C. Schmidt.Ph.D