The BABAR Collaboration BABAR, the detector for the SLAC PEP-II asymmetric e + e − B Factory operating at the Υ (4S) resonance, was designed to allow comprehensive studies of CP -violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems , VME-and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

The use of N-heterocyclic carbenes (NHCs) in chemistry has developed rapidly over the past twenty years. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centres, and as organocatalysts able to mediate an exciting range of reactions. However, the sheer number of NHCs known in the literature can make the appropriate choice of NHC for a given application difficult. A number of metrics have been explored that allow the electronic properties of NHCs to be quantified and compared. In this review, we discuss these various metrics and what they can teach about the electronic properties of NHCs. Data for approximately three hundred NHCs are presented, obtained from a detailed survey of the literature.

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The relationship between the NMR chemical shifts of phosphinidene and selenourea compounds and the π-accepting ability of the related carbene ligands has been investigated.