De spectric electroniorum secundariorum prorsus rectorum e corporibus solidis ioniis penetrantibus inductorum

Summary A short introduction into the phenomenon of kinetic ioninduced secondary electron emission from solids is given. The basic features of proton-induced secondary electron spectra from thin foils in forward-(beam-) direction are briefly discussed.

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Summarium Post brevem introductionem in phaenomenon emissionis cineticae electroniorum secundariorum ioniis inductae e corporibus solidis structurae praevalentes spectrorum energiae electroniorum secundariorum ex foliis tenibus protoniis inductorum prorsus rectorum, id est in directionem radii, proponuntur.

     

A mobile positron-lifetime spectrometer for field applications based on β+-γ coincidence

+ -γ coincidence measurement, which has been applied to in-situ examinations of microstructural evolution processes during the fatigue of copper single crystals, is described. Since no sandwich-type geometry is required, it is applicable to all specimen geometries commonly used in materials testing and to the non-destructive testing of engineering parts in service. As a radioactive source ⁷²Se generates the positron-emitting ⁷²As, which provides two positron spectra with maximum energies of 2.5 MeV and 3.3 MeV and a prompt γ quantum of 835 keV. The positrons emitted in the direction towards the specimen pass through a fast plastic scintillator and produce a scintillation signal, thereby losing about 150 keV of their energy. This signal serves as a start signal for the positron-lifetime measurement and is measured in coincidence with the subsequent 511 keV annihilation quantum. After passage through the plastic scintillator the remaining positron energy is still high enough to penetrate deep into the material and to allow for real bulk examinations. The prompt γ quantum may serve as an on-line control of the stability of the electronic system which will be useful under non-constant service conditions in a proposed field application. Received: 8 January 1997/Accepted: 14 March 1997     

A study of high spin states in the transitional nucleus90Mo

The reaction⁵⁸Ni(³⁶Ar, 4p)⁹⁰Mo has been studied at a beam energy of 149 MeV. A detector array consisting of the OSIRIS spectrometer (12 Compton-suppressed Ge detectors), four charged-particleδE detectors and seven NE-213 neutron detectors at the VICKSI accelerator in Berlin has been used to measure the gamma radiation inγγ- and particle-γγ-coincidence mode. An additional Ge detector was placed at 162? to the beam direction to provide information on DCO ratios. The level scheme of⁹⁰Mo has been extended up to an excitation energy of about 12 MeV and probable spin 23?. Some 70 transitions and 40 levels have been newly identified. Spin assignments have been proposed on the basis of measured DCO ratios. Shell model calculations in a model space consisting of the proton 1f _5/2, 2p _3/2, 2p _1/2, and 1g _9/2 orbits and the neutron 2p _1/2, 1g _9/2, 1g _7/2, 2d _5/2, 2d _3/2, and 3s _1/2 orbits with some truncation were made for states above 9? and the predicted structure of these states is discussed.     

Biology‐Oriented Synthesis of a Withanolide‐Inspired Compound Collection Reveals Novel Modulators of Hedgehog Signaling

Biology‐oriented synthesis employs the structural information encoded in complex natural products to guide the synthesis of compound collections enriched in bioactivity. The trans‐hydrindane dehydro‐δ‐lactone motif defines the characteristic scaffold of the steroid‐like withanolides, a plant‐derived natural product class with a diverse pattern of bioactivity. A withanolide‐inspired compound collection was synthesized by making use of three key intermediates that contain this characteristic framework derivatized with different reactive functional groups. Biological evaluation of the compound collection in cell‐based assays that monitored biological signal‐transduction processes revealed a novel class of Hedgehog signaling inhibitors that target the protein Smoothened.     

Enantiomeric separation of 1,3‐dimethylamylamine by capillary electrophoresis with indirect UV detection using a dual‐selector system

The CE method employing an indirect UV detection for the enantioseparation of 1,3‐dimethylamylamine (DMAA), widely used in various preworkout and dietary supplements labeled as a constituent of geranium extract has been developed. The dual‐selector system consisting of negatively charged sulfated α‐CD (1.1% w/v) and sulfated β‐CD (0.2% w/v) in 5 mM phosphate/Tris buffer (pH 3.0) containing the addition of 10 mM benzyltriethylammonium chloride (BTEAC) as the chromophoric additive was used for the enantiomeric separation of DMAA stereoisomers with the LODs in the range of 7.82–9.24 μg/mL. The method was partly validated and applied for the determination of the stereoisomeric composition of DMAA in commercial dietary supplements to verify the potential natural origin of DMAA.     

On the Wiener–Hopf Method for Surface Plasmons: Diffraction from Semiinfinite Metamaterial Sheet

By formally invoking the Wiener–Hopf method, we explicitly solve a one‐dimensional, singular integral equation for the excitation of a slowly decaying electromagnetic wave, called surface plasmon‐polariton (SPP), of small wavelength on a semiinfinite, flat conducting sheet irradiated by a plane wave in two spatial dimensions. This setting is germane to wave diffraction by edges of large sheets of single‐layer graphene. Our analytical approach includes (i) formulation of a functional equation in the Fourier domain; (ii) evaluation of a split function, which is expressed by a contour integral and is a key ingredient of the Wiener–Hopf factorization; and (iii) extraction of the SPP as a simple‐pole residue of a Fourier integral. Our analytical solution is in good agreement with a finite‐element numerical computation.