Beam Position Determination using Tracks

Track-based algorithms to determine the LHC beam position and profile at the CMS collision point are described. Only track information is used and no reconstruction of the primary event vertex is required. With only about thousand tracks, a statistical precision of 2 microns for the transverse beam position is achieved, assuming a well aligned detector. The algorithms are simple and fast, and can be used to monitor the beam in real time. A method to determine the track impact parameter resolution using the beam position and beam width calculation is also presented

Fe Protein-Independent Substrate Reduction by Nitrogenase MoFe Protein Variants

The reduction of substrates catalyzed by nitrogenase normally requires nucleotide-dependent Fe protein delivery of electrons to the MoFe protein, which contains the active site FeMo cofactor. Here, it is reported that independent substitution of three amino acids (β- 98Tyr→His, α-64Tyr→His, and β-99Phe→His) located between the P cluster and FeMo cofactor within the MoFe protein endows it with the ability to reduce protons to H2, azide to ammonia, and hydrazine to ammonia without the need for Fe protein or ATP. Instead, electrons can be provided by the low-potential reductant polyaminocarboxylate-ligated Eu(II) (Em values of −1.1 to −0.84 V vs the normal hydrogen electrode). The crystal structure of the β-98Tyr→His variant MoFe protein was determined, revealing only small changes near the amino acid substitution that affect the solvent structure and the immediate vicinity between the P cluster and the FeMo cofactor, with no global conformational changes observed. Computational normal-mode analysis of the nitrogenase complex reveals coupling in the motions of the Fe protein and the region of the MoFe protein with these three amino acids, which suggests a possible mechanism for how Fe protein might communicate subtle changes deep within the MoFe protein that profoundly affect intramolecular electron transfer and substrate reduction