Operation and performance of the ATLAS Tile Calorimeter in Run 1

The Tile Calorimeter is the hadron calorimeter covering the central region of the ATLAS experiment at the Large Hadron Collider. Approximately 10,000 photomultipliers collect light from scintillating tiles acting as the active material sandwiched between slabs of steel absorber. This paper gives an overview of the calorimeter’s performance during the years 2008–2012 using cosmic-ray muon events and proton–proton collision data at centre-of-mass energies of 7 and 8TeV with a total integrated luminosity of nearly 30 fb−1. The signal reconstruction methods, calibration systems as well as the detector operation status are presented. The energy and time calibration methods performed excellently, resulting in good stability of the calorimeter response under varying conditions during the LHC Run 1. Finally, the Tile Calorimeter response to isolated muons and hadrons as well as to jets from proton–proton collisions is presented. The results demonstrate excellent performance in accord with specifications mentioned in the Technical Design Report

Formation of Highly Ordered Spherical Aggregates from Drying Microdroplets of Colloidal Suspension

The formation of highly ordered spherical aggregates of silica nanoparticles by the evaporation of single droplets of an aqueous colloidal suspension levitated (confined) in the electrodynamic quadrupole trap is reported. The transient and final structures formed during droplet evaporation have been deposited on a silicon substrate and then studied with SEM. Various successive stages of the evaporation-driven aggregation of nanoparticles have been identified: formation of the surface layer of nanoparticles, formation of the highly ordered spherical structure, collapse of the spherical surface layer leading to the formation of densely packed spherical aggregates, and rearrangement of the aggregate into the final structure of a stable 3D quasi-crystal. The evaporation-driven aggregation of submicrometer particles in spherical symmetry leads to sizes and morphologies of the transient and final structures significantly different than in the case of aggregation on a substrate. The numerical model presented in the article allows us to predict and visualize the observed aggregation stages and their dynamics and the final aggregates observed with SEM

Rational and Then Serendipitous Formation of Aza Analogues of Hoveyda-Type Catalysts Containing a Chelating Ester Group Leading to a Polymerization Catalyst Family

Analogues of the well-known Hoveyda–Grubbs catalyst bearing both a chelating ester function and a chelating nitrogen atom were obtained. These complexes behave differently depending on the character of the chelating amine. Complexes containing a secondary amine underwent unexpected spontaneous oxidation of the amine group, leading to the Schiff base analogues. In contrast, complexes containing a tertiary amine were prone to intramolecular cyclization in the presence of a base (Et₃N). Probing the activity of such (pre)­catalysts in ring-closing metathesis reactions (RCMs) revealed their dormant character and excellent thermo-switchability. In particular, complexes bearing an iminium nitrogen fragment were found to be very useful in a delayed ring-opening metathesis polymerization (ROMP) and were therefore commercialized

Solid State Structural Variations in Copper(II) Complexes of Open-Chain and Macrocyclic Malonamide-Derived Ligands

An analysis of the molecular structure of the copper­(II) complexes with open-chain and macrocyclic malonamide-derived tetradentate ligands based on single crystal X-ray diffraction study of four copper­(II) complexes [CuL¹(H₂O)]·4H₂O, [CuL²(H₂O)], [CuL³(H₂O)], and [CuL⁴(H₂O)] (H₂L¹<b> = </b>1,4,8,11-tetraazaundecane-5,7-dione, H₂L² = 13-methyl-13-nitro-1,4,8,11-tetraazacyclotetradecane-5,7-dione, H₂L³ = 1,4,8,11-tetraazacyclotetradecane-5,7-dione, and H₂L⁴ = 1,4,8,11-tetraazacyclotridecane-5,7-dione) as well as on published data regarding related compounds revealed that the violations of planarity of the metal-amide fragments are due almost exclusively to the deviation of the copper­(II) ion from the amide plane. Both the deviation of the copper­(II) ion from the amide plane and the angle between amide planes in the 6-membered malonamide ring are strongly affected by substituents with minimal values observed in the complexes of unsubstituted ligands. The deviation of the copper­(II) ion from the basal plane of donor atoms was shown to relate to the sum of bite angles around the copper­(II) ion and roughly correlates to Cu–L_ax distances when apical ligands are present. The crystals of the macrocyclic complexes CuL² to CuL⁴ are built up from similar corrugated layers in which metal complex molecules are linked in a “head-to-tail” manner <i>via</i> NH···OC hydrogen bonds. In contrast, [CuL¹(H₂O)]·4H₂O has a lamellar crystal structure in which the layers built up of [CuL¹(H₂O)] units alternate with sheets formed by water molecules

Using Molecular Dynamics and Quantum Mechanics Calculations To Model Fluorescence Observables

We provide a critical examination of two different methods for generating a donoracceptor electronic coupling trajectory from a molecular dynamics (MD) trajectory and three methods for sampling that coupling trajectory, allowing the modeling of experimental observables directly from the MD simulation. In the first coupling method we perform a single quantum-mechanical (QM) calculation to characterize the excited state behavior, specifically the transition dipole moment, of the fluorescent probe, which is then mapped onto the configuration space sampled by MD. We then utilize these transition dipoles within the ideal dipole approximation (IDA) to determine the electronic coupling between the probes that mediates the transfer of energy. In the second method we perform a QM calculation on each snapshot and use the complete transition densities to calculate the electronic coupling without need for the IDA. The resulting coupling trajectories are then sampled using three methods ranging from an independent sampling of each trajectory point (the independent snapshot method) to a Markov chain treatment that accounts for the dynamics of the coupling in determining effective rates. The results show that the IDA significantly overestimates the energy transfer rate (by a factor of 2.6) during the portions of the trajectory in which the probes are close to each other. Comparison of the sampling methods shows that the Markov chain approach yields more realistic observables at both high and low FRET efficiencies. Differences between the three sampling methods are discussed in terms of the different mechanisms for averaging over structural dynamics in the system. Convergence of the Markov chain method is carefully examined. Together, the methods for estimating coupling and for sampling the coupling provide a mechanism for directly connecting the structural dynamics modeled by MD with fluorescence observables determined through FRET experiments