Measurement of the solenoid magnetic field

We describe the machine used to map the solenoid field and the data sets that were collected. The bulk of the note describes the analysis of this data. A series of small corrections are made; some taken from surveys and some derived from the data itself. Two fitting methods are defined and applied to all data sets. The final result is that the field map at normal operating current can be fitted to a function that obeys Maxwell with an r.m.s. residual of less than 5 Gauss. Systematic errors on the measurement of track sagitta due to the field uncertainty are estimated to be in the range 2.3E-4 to 12E-4, depending on the track rapidity. Finally, the representation of the map in Athena is briefly described

Measurement of the ATLAS solenoid magnetic field

ATLAS is a general purpose detector designed to explore a wide range of physics at the Large Hadron Collider. At the centre of ATLAS is a tracking detector in a 2 T solenoidal magnetic field. This paper describes the machine built to map the field, the data analysis methods, the final results, and their estimated uncertainties. The remotely controlled mapping machine used pneumatic motors with feedback from optical encoders to scan an array of Hall probes over the field volume and log data at more than 20 000 points in a few hours. The data were analysed, making full use of the physical constraints on the field and of our knowledge of the solenoid coil geometry. After a series of small corrections derived from the data itself, the resulting maps were fitted with a function obeying Maxwell's equations. The fit residuals had an r.m.s. less than 0.5 mT and the systematic error on the measurement of track sagitta due to the field uncertainty was estimated to be in the range 0.02 % to 0.12 % depending on the track rapidity

Using a 2D detector array for meaningful and efficient linear accelerator beam property validations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135512/1/acm20046.pd

TG‐69: Radiographic film for megavoltage beam dosimetry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134818/1/mp6779.pd

EGFR oligomerization organizes kinase-active dimers into competent signalling platforms

Epidermal growth factor receptor (EGFR) signalling is activated by ligand-induced receptor dimerization. Notably, ligand binding also induces EGFR oligomerization, but the structures and functions of the oligomers are poorly understood. Here, we use fluorophore localization imaging with photobleaching to probe the structure of EGFR oligomers. We find that at physiological epidermal growth factor (EGF) concentrations, EGFR assembles into oligomers, as indicated by pairwise distances of receptor-bound fluorophore-conjugated EGF ligands. The pairwise ligand distances correspond well with the predictions of our structural model of the oligomers constructed from molecular dynamics simulations. The model suggests that oligomerization is mediated extracellularly by unoccupied ligand-binding sites and that oligomerization organizes kinase-active dimers in ways optimal for auto-phosphorylation in trans between neighbouring dimers. We argue that ligand-induced oligomerization is essential to the regulation of EGFR signalling

Biologically inspired simulation of livor mortis

We present a biologically motivated livor mortis simulation that is capable of modelling the colouration changes in skin caused by blood pooling after death. Our approach consists of a simulation of post mortem blood dynamics and a layered skin shader that is controlled by the haemoglobin and oxygen levels in blood. The object is represented by a layered data structure made of a triangle mesh for the skin and a tetrahedral mesh on which the blood dynamics are simulated. This allows us to simulate the skin discolouration caused by livor mortis, including early patchy appearance, fixation of hypostasis and pressure induced blanching. We demonstrate our approach on two different models and scenarios and compare the results to real world livor mortis photographic examples

Effect of Spermidine on Misfolding and Interactions of Alpha-Synuclein

Alpha-synuclein (α-Syn) is a 140 aa presynaptic protein which belongs to a group of natively unfolded proteins that are unstructured in aqueous solutions. The aggregation rate of α-Syn is accelerated in the presence of physiological levels of cellular polyamines. Here we applied single molecule AFM force spectroscopy to characterize the effect of spermidine on the very first stages of α-Syn aggregation – misfolding and assembly into dimers. Two α-Syn variants, the wild-type (WT) protein and A30P, were studied. The two protein molecules were covalently immobilized at the C-terminus, one at the AFM tip and the other on the substrate, and intermolecular interactions between the two molecules were measured by multiple approach-retraction cycles. At conditions close to physiological ones at which α-Syn misfolding is a rare event, the addition of spermidine leads to a dramatic increase in the propensity of the WT and mutant proteins to misfold. Importantly, misfolding is characterized by a set of conformations, and A30P changes the misfolding pattern as well as the strength of the intermolecular interactions. Together with the fact that spermidine facilitates late stages of α-Syn aggregation, our data demonstrate that spermidine promotes the very early stages of protein aggregation including α-Syn misfolding and dimerization. This finding suggests that increased levels of spermidine and potentially other polyamines can initiate the disease-related process of α-Syn

Dystroglycan versatility in cell adhesion: a tale of multiple motifs

Dystroglycan is a ubiquitously expressed heterodimeric adhesion receptor. The extracellular a-subunit makes connections with a number of laminin G domain ligands including laminins, agrin and perlecan in the extracellular matrix and the transmembrane b-subunit makes connections to the actin filament network via cytoskeletal linkers including dystrophin, utrophin, ezrin and plectin, depending on context. Originally discovered as part of the dystrophin glycoprotein complex of skeletal muscle, dystroglycan is an important adhesion molecule and signalling scaffold in a multitude of cell types and tissues and is involved in several diseases. Dystroglycan has emerged as a multifunctional adhesion platform with many interacting partners associating with its short unstructured cytoplasmic domain. Two particular hotspots are the cytoplasmic juxtamembrane region and at the very carboxy terminus of dystroglycan. Regions which between them have several overlapping functions: in the juxtamembrane region; a nuclear localisation signal, ezrin/radixin/moesin protein, rapsyn and ERK MAP Kinase binding function, and at the C terminus a regulatory tyrosine governing WW, SH2 and SH3 domain interactions. We will discuss the binding partners for these motifs and how their interactions and regulation can modulate the involvement of dystroglycan in a range of different adhesion structures and functions depending on context. Thus dystroglycan presents as a multifunctional scaffold involved in adhesion and adhesion-mediated signalling with its functions under exquisite spatiotemporal regulation