Biological evaluation of ent-narciclasine, ent-lycoricidine, and certain enantiomerically-related congeners

The non-natural enantiomeric forms of narciclasine and lycoricidine ((-)-1 and (-)-2, respectively), as well as congeners 3-6 are available through chemoenzymatic synthesis. Accordingly, they have now been tested for their cytotoxic effects in a 13-member human cancer cell-line panel and found to be only weakly active. In contrast, an authentic sample of the natural enantiomeric form of narciclasine ((+)-1) was found to be highly active in the same screens

Precise Measurement of Small Currents at the MLS

The Physikalisch Technische Bundesanstalt PTB , the National Metrology Institute of Germany, utilizes an electron storage ring the Metrology Light Source MLS , located in Berlin, as a radiation source standard in the VIS, UV and VUV spectral range. In order to be able to calculate the absolute intensity of the radiation, the electron beam current has to be measured with low uncertainty. In this paper we focus on the measurement of the beam current in a range of several nA to 1 pA one electron by means of Si photodiodes, detecting synchrotron radiation from the beam. Electrons are gradually scraped out of the ring and the diode signal is analyzed afterwards. The exact number of stored electrons then can be derived from the signal. The measurement is carried out automatically with an in house developed softwar

Experimental demonstration of the mechanism of steady state microbunching

The use of particle accelerators as photon sources has enabled advances in science and technology1. Currently the workhorses of such sources are storage ring based synchrotron radiation facilities2,3,4 and linear accelerator based free electron lasers5,6,7,8,9,10,11,12,13,14. Synchrotron radiation facilities deliver photons with high repetition rates but relatively low power, owing to their temporally incoherent nature. Free electron lasers produce radiation with high peak brightness, but their repetition rate is limited by the driving sources. The steady state microbunching15,16,17,18,19,20,21,22 SSMB mechanism has been proposed to generate high repetition, high power radiation at wavelengths ranging from the terahertz scale to the extreme ultraviolet. This is accomplished by using microbunching enabled multiparticle coherent enhancement of the radiation in an electron storage ring on a steady state turn by turn basis. A crucial step in unveiling the potential of SSMB as a future photon source is the demonstration of its mechanism in a real machine. Here we report an experimental demonstration of the SSMB mechanism. We show that electron bunches stored in a quasi isochronous ring can yield sub micrometre microbunching and coherent radiation, one complete revolution after energy modulation induced by a 1,064 nanometre wavelength laser. Our results verify that the optical phases of electrons can be correlated turn by turn at a precision of sub laser wavelengths. On the basis of this phase correlation, we expect that SSMB will be realized by applying a phase locked laser that interacts with the electrons turn by turn. This demonstration represents a milestone towards the implementation of an SSMB based high repetition, high power photon sourc