For more than 25 years, the Physikalisch‐Technische Bundesanstalt has been strongly engaged in the field of metrology using synchrotron radiation. In Berlin, this research programme started together with the user operation of the electron storage ring BESSY I in the early 1980s. At the beginning, the work was focused on fundamental radiometry, i.e. using the storage ring as a primary radiation source standard and operating beamlines for source and detector calibration in the vacuum ultraviolet spectral range. Meanwhile, at the electron storage rings BESSY II and Metrology Light Source in Berlin‐Adlershof, the activities have been extended to a broad range of fundamental and applied photon metrology in the range from the far infrared to hard X‐rays, including methods like cryogenic radiometry, reflectometry and X‐ray fluorescence spectroscopy. In the present review, we give a short historical introduction to this work, describe our laboratories and the basic radiometric principles, and present examples of recent applications, largely performed within the framework of scientific cooperations with external partners from industry and research. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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The Metrology Light Source (MLS), the new electron storage ring of the Physikalisch-Technische Bundesanstalt (PTB) located in Berlin, is dedicated to metrology and technological developments in the UV and extreme UV spectral range as well as in the IR and THz region. The MLS can be operated at any electron beam energy between 105 and 630 MeV and at electron beam currents varying from 1 pA (one stored electron) up to 200 mA. Moreover, it is optimized for the generation of coherent synchrotron radiation in the far IR/THz range. Of special interest for PTB is the operation of the MLS as a primary radiation source standard from the near IR up to the soft x-ray region. Therefore, the MLS is equipped with all the instrumentation necessary to measure the storage ring parameters and geometrical parameters needed for the calculation of the spectral photon flux according to the Schwinger theory with low uncertainty.

The Metrology Light Source is a recently constructed 630 MeV electron storage ring, operating as a synchrotron radiation source for the THz to extreme UV spectral range. It is the first storage ring optimized for generating intense, broadband, coherent THz radiation, based on a bunch shortening mode. Stable (''steady state'') or bursting THz radiation up to an average power of about 60 mW can be obtained. The applied machine operation mode is achieved by manipulating the momentum compaction factor by a novel tuning scheme. The underlying low-scheme is of general interest for operating a storage ring in a short bunch mode and is the main subject of this paper.

The B cell antigen receptor (BCR) is a multiprotein complex consisting of the membrane-bound Ig molecule and the Ig-␣͞Ig-␤ heterodimer. On BCR engagement, Ig-␣ and Ig-␤ become phosphorylated not only on tyrosine residues of the immunoreceptor tyrosine-based activation motif but also on serine and threonine residues. We have mutated all serine and threonine residues in the Ig-␣ tail to alanine and valine, respectively. The mutated Ig-␣ sequence was expressed either as a single-chain Fv͞Ig-␣ molecule or in the context of the complete BCR. In both cases, the mutated Ig-␣ showed a stronger tyrosine phosphorylation than the wildtype Ig-␣ and initiated increased signaling on stimulation. These findings suggest that serine͞threonine kinases can negatively regulate signal transduction from the BCR. T he members of the multisubunit immune recognition receptor family have similarities in their structure and share signal transduction pathways (1, 2). Prominent members of this family are the B cell antigen receptor (BCR), the T cell antigen receptor (TCR), and the high-affinity IgE receptor (FcRI). These receptors consist of a ligand-binding part and signaling subunits carrying an immunoreceptor tyrosine-based activation motif (ITAM; refs. 1 and 3). Studies on the BCR suggest that, already in the absence of the ligand, the receptor is associated with a preformed transducer complex comprising intracellular kinases, phosphatases, and adaptor molecules (4). Engagement of the receptor results in the activation of protein tyrosine kinases (PTKs), which phosphorylate several intracellular substrate proteins including the adapter protein SLP-65 (also called BLNK or BASH; refs. 5-7) and the Ig-␣͞Ig-␤ heterodimer (8). The ITAM sequence of Ig-␤, however, is less efficiently tyrosine phosphorylated than that of Ig-␣, and the reason for this difference is not known thus far (9, 10). After phosphorylation, the ITAM tyrosines become binding targets for proteins with Src homology 2 (SH2) domains (11)(12)(13)(14). The best studied interaction is that of the two tandem-arranged SH2 domains of the PTK Syk with the phosphorylated ITAM tyrosines of CD3-(15). The binding of Syk to the ITAM results in an increased kinase activity (16-18). The Syk-associated BCR is efficiently internalized and transported to endosomal compartments where antigen processing occurs (19). Syk binding and activity is also required for endocytosis of ITAM-containing Fc receptors in macrophages (20,21).BCR engagement results not only in tyrosine phosphorylation but also in increased serine and threonine phosphorylation. Because of the lack of universal anti-phosphoserine or antiphosphothreonine antibodies, the latter events are poorly studied and require laborious biochemical techniques for their detection. Phosphorylation of serine͞threonine residues occurs in the cytoplasmic sequence of many receptors or their signaltransducing elements and can have either positive or negative effects on signal transduction through these receptors (22-26). The cytoplasmic tails of Ig-...

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The Physikalisch-Technische Bundesanstalt (PTB) has set up the 630 MeV electron storage ring Metrology Light Source (MLS) in close cooperation with the Helmholtz-Zentrum Berlin (HZB). This electron storage ring has been in regular user operation since April 2008. It is dedicated to synchrotron-radiation-based metrology and technological developments in the far-IR/THz, IR, UV, VUV and EUV spectral ranges, with the use as primary source standard as the key activity. In a permanent process of improvement, the storage ring itself was optimized regarding its regular performance (beam current and lifetime) as well as for special operations (e.g. variable electron energies and electron bunch lengths). The measurement capabilities at the seven different beamline ports were set up sequentially, first in the UV/VUV and IR spectral ranges. This first phase of instrumentation set-up will be finished in 2011 by completing the beamlines for EUV metrology, for the calibration of radiation sources and for the application of undulator radiation.

Membrane-bound immunoglobulin (mIg) of the IgG, IgA, and IgE classes have conserved cytoplasmic tails. To investigate the function of these tails, a B cell line was transfected with truncated or mutated gamma2a heavy chains. Transport to the endosomal compartment of antigen bound by the B cell antigen receptor did not occur in the absence of the cytoplasmic tail; and one or two mutations, respectively, in the Tyr-X-X-Met motif of the tail partially or completely interrupted the process. Experiments with chimeric antigen receptors confirmed these findings. Thus, a role for the cytoplasmic tail of mIg heavy chains in endosomal targeting of antigen is revealed.