Crystal calorimeters in the next decade

Crystal calorimeter has traditionally played an important role in precision measurement of electrons and photons in high energy physics experiments. Recent interest in calorimeter technology extends its application to measurement of hadrons and jets with dual readout. Potential application of new generation scintillating crystals of high density and high light yield, such as LYSO, in high energy physics experiments is described. Candidate crystals for the homogeneous hadronic calorimeter concept are also discussed

Precision Crystal Calorimeters in High Energy Physics: Past, Present and Future

Precision crystal calorimeters traditionally play an important role in high energy physics experiments. In the last two decades, it faces a challenge to maintain its precision in a hostile radiation environment. This paper reviews the performance of crystal calorimeters constructed for high energy physics experiments and the progress achieved in understanding crystal's radiation damage as well as in developing high quality scintillating crystals for particle physics. Potential applications of new generation scintillating crystals of high density and high light yield, such as LSO and LYSO, in particle physics experiments is also discussed

The Next Generation of Crystal Detectors

Heavy crystal scintillators are used widely in HEP experiments for precision measurements of photons and electrons. Future HEP experiments, however, require crystal scintillators of more bright, more fast, more radiation hard and less cost. This paper discusses several R&D directions for the next generation of crystal detectors for future HEP experiments.Comment: 5 pages, 2 tables, white paper for the 2013 DPF Snowmass Summer Stud

Atomic and magnetic structures of (CuCl)LaNb2_2O7_7 and (CuBr)LaNb2_2O7_7: Density functional calculations

The atomic and magnetic structures of (Cu$X$)LaNb$_2$O$_7$ ($X$=Cl and Br) are investigated using the density-functional calculations. Among several dozens of examined structures, an orthorhombic distorted $2\times 2$ structure, in which the displacement pattern of $X$ halogens resembles the model conjectured previously based on the empirical information is identified as the most stable one. The displacements of $X$ halogens, together with those of Cu ions, result in the formation of $X$-Cu-$X$-Cu-$X$ zigzag chains in the two materials. The nearest-neighbor interaction within the zigzag chains are determined to be antiferromagnetic (AFM) for (CuCl)LaNb$_2$O$_7$ but ferromagnetic (FM) for (CuBr)LaNb$_2$O$_7$. On the other hand, the first two neighboring interactions between the Cu cations from adjacent chains are found to be AFM and FM respectively for both compounds. The magnitudes of all these in-plane exchange couplings in (CuBr)LaNb$_2$O$_7$ are evaluated to be about three times those in (CuCl)LaNb$_2$O$_7$. In addition, a sizable AFM inter-plane interaction is found between the Cu ions separated by two NbO$_6$ octahedra. The present study strongly suggests the necessity to go beyond the square $J_1-J_2$ model in order to correctly account for the magnetic property of (Cu$X)$LaNb$_2$O$_7$.Comment: 24 pages, 7 figure

Morphological Changes of Neuronal Growth Cones by Intracellular Signaling and Cell Culture Conditions

Proper wiring of neurons is key to the functionality of nervous system. This is achieved by a highly motile structure referred to as the neuronal growth cone located at the tip of axons and dendrites during both development and regeneration. The morphology of growth cone is a product of both intracellular signaling pathways and extracellular factors, and is closely linked with neuronal outgrowth. Studies of how growth cone morphology is changed by key regulatory proteins and by cell culture conditions are therefore important in elucidating the mechanisms of neurite regeneration. In the first part of this thesis, we identified a single tyrosine residue (Y499) in Aplysia cortactin that is important for regulating filopodia formation in growth cone. Overexpression of the 499F phospho-deficient cortactin mutant decreased filopodia length and density, whereas overexpression of the 499E phospho-mimetic mutant increased filopodia length, regardless of the phosphorylation state of Y505 or Y509. Using a custom-made antibody against cortactin phosphorylated at Y499, we showed that phosphorylated cortactin is enriched in the peripheral domain, specifically along the leading edge. We found that treatment with the Src inhibitor PP2 decreased cortactin phosphorylation, while overexpression of Src2 increased cortactin phosphorylation. We demonstrated that the leading edge localization of phosphorylated cortactin is F-actin independent, and important in promoting filopodia formation. Finally, by interfering both with cortactin phosphorylation and Arp2/3 activation, we found that Arp2/3 complex acts downstream of cortactin to regulate filopodia density but not length. In conclusion, we have characterized a tyrosine phosphorylation site in Aplysia cortactin that plays a major role in the Src/cortactin/Arp2/3 signaling pathway controlling filopodia formation. In the second part of this thesis, we offer a comprehensive cellular analysis of the motile behavior of Aplysia growth cones on two-dimensional (2D) culture beyond the pausing state. We found that average growth cone size decreased with cell culture time whereas average growth rate increased. This inverse correlation of growth rate and growth cone size was due to the occurrence of large growth cones with a peripheral domain larger than 100 μm2. The large pausing growth cones had central domains that were less consistently aligned with the direction of growth and could be converted into smaller, faster-growing growth cones by addition of a three-dimensional (3D) collagen gel. We conclude that the significant lateral expansion of lamellipodia and filopodia as observed during these culture conditions has a negative effect on neurite growth. Further, using the novel collagen gel and an easy-to-make microwell device, we developed a simple protocol for 3D culture of Aplysia bag cell neuron. We found that the morphology and growth pattern of bag cell growth cones in 3D culture closely resemble the ones of growth cones observed in vivo, and demonstrated the capability of our device for high-resolution imaging of cytoskeletal and signaling proteins as well as organelles. We expect that our microwell device will facilitate a wider adoption of 3D neuronal cultures to study the mechanisms of neurite regeneration