[en] The author has studied the reaction e⁺e^- → e⁺e^-γγ → e⁺e^- + hadrons using the Time Projection Chamber (TPC) at the PEP storage ring at Stanford Linear Accelerator Center (SLAC). The final state particles are identified by measuring their ionization energy loss rate (dE/dx) and momentum. The data sample corresponds to an integrated luminosity of 67 pb^-1 at √s = 29 GeV where only events containing a single tag with Q² ≥ 0.03 GeV² are considered. The Quark Parton Model (QPM) and Vector-meson Dominant Model (VDM) are used to explain the hadron productions in twophoton process. We use the Lund 5.3 for the quark fragmentation. The fractions of π^±, K^± and p bar p are studied in both data and Monte Carlo events. The data shows the γγ characteristic in favor of the VDM. No significant evidence has been found for the charm threshold in two-photon process at √s = 29 GeV

[en] The critical temperature (T_c) changes related to the microstructure as a function of annealing temperature for a BiSrCaCuO (BSCCO) film implanted with 170 keV P⁺ at two different doses were studied. The BSCCO films were prepared by d.c. sputtering on MgO substrates. For the film implanted at a dose of 5 x 10¹⁵ cm^-2, post-implantation annealing at 600-800^oC enabled the T_cs of the film to be completely recovered. For the film implanted at a dose of 1.0 x 10¹⁷ cm^-2 the T_cs were only partly recovered after 600^oC annealing. On further annealing at 700^oC the superconductivity of the film disappeared. Transmission electron microscopy showed that a significant amount of CaP, Ca₃P2, and some unknown phases was formed. It is considered that these phases formed during post-implantation annealing render the recovery of the superconductivity of the P⁺-implanted BSCCO film difficult. (author)

[en] The microstructure of Y-Ba-Cu-O compound, sintered at 950⁰C for 16h, was examined by using transmission electron microscope (TEM). For the furnace cooling sample, two variants of orthorhombic YBa/sub 2/Cu/sub 3/O/sub 7-x/ (O-Y123) twins, grown on (110) and (110 planes, respectively, are crystallographically related to the matrix and produce a Widmanstatten morphology. The orientation relationships between the lath twin and the matrix is (001)/sub T///(001)/sub M/ and [010]/sub M/. The O-123 compound is unstable under the electron irradiation. Twin boundaries are identified as δ-boundaries. The minor phases as Y/sub 2/BaCuO/sub 5/(Y211) and BaCuO/sub 2/ were also observed. For the air cooling sample, no superconductivity above 77K was found. The major phase is tetragonal Y123 (T-Y123), while a small amount of O-Y123 is also existent

[en] The formation of Y-Ba-Cu-O phases, including the high Tc superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ (Y123) phase, during solid state reaction of the mixture of Y/sub 2/O/sub 3/: BaCO/sub 3/: CuO, in molar ratio of 0.2:0.6:1 to conform the formula of the perovskite (Y/sub 0.4/Ba/sub 0.6/)CuO/sub 3/ composition was studied by means of DTA, DTG and X-ray diffractometry (XRD). For continuous heating at 10 C/min, it was found that the Y123 phase exists at 790-995 C, and gradually disappears at higher temperatures. The insulating Y/sub 2/BaCuO/sub 5/ (Y211) phase exists at 985 to 1190 C, the maximum experiment temperature. While the semiconducting YBa/sub 3/Cu/sub 2/O/sub 7-y/ (Y132) phase coexists with the Y123 phase. For isothermal heating, it was found that the most appropriate temperature and time for the formation of the Y123 phase is 900⁰C and 16 hours. Semiquantitative data on the amount of phases presented, including the above mentioned phases and other binary Ba-Y-O or Ba-Cu-O phases, during heating are also given. High temperature superconductor with a Tc of around 93 K can be synthesized reproducibly by the processes based on this study

[en] BiSrCaCuO film was deposited on (100)MgO using DC sputtering method. The degree of transformation from 221 phase to 2212 phase was detected by x-ray diffraction analysis. A series of measurements under isothermal conditions at different temperatures were performed on one specimen. The kinetic parameters such as reaction order and activation energy were obtained using the Johnson-Mehl-Avrami equation

[en] The production of δ-ray electrons in silicon strip tracking systems is measured for electrons in the energy range of 2-50 GeV. The results are compared to GEANT calculations. The production cutoff threshold is calibrated, and a value of T_cut=3D500 keV is chosen. The δ-ray angular distribution is measured for electrons transmitting through a 320 μm silicon wafer. The δ-ray production rate is approximately 1.3% within an angular region of 1-50 mrad. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] The performance of silicon microstrip detectors in electron and pion beams of momenta up to 50 GeV has been studied. Results are compared to full GEANT simulations. The energy loss straggling in silicon wafers is compared to the Urban and PAI models. Productions of delta-ray electrons and electron-positron pairs by 50 GeV electrons, seen as multi-cluster events, are compared to GEANT calculations. The spatial resolution is determined with the detector intrinsic resolution simulated by Gaussian smearing and the multiple scattering calculated by Moliere theory. The deflection due to multiple scattering in crystalline structure was investigated by placing a GaAs wafer at various angles between active detectors. Larger deflection is seen in data of inclined tracks at 45 to the silicon crystalline plane. (orig.)

[en] The PHOBOS experiment is well positioned to obtain crucial information about relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC), combining a multiplicity counter with a multi-particle spectrometer. The multiplicity arrays will measure the charged-particle multiplicity over the full solid angle. The spectrometer will be able to identify particles at mid-rapidity. The experiment is constructed almost exclusively of silicon pad detectors. Detectors of nine different types are configured in the multiplicity and vertex detector (22,000 channels) and two multi-particle spectrometers (120,000 channels). The overall layout of the experiment, testing of the silicon sensors and the performance of the detectors during the engineering run at RHIC in 1999 are discussed

[en] The analysis on test beam data of a large silicon microstrip detector is presented. The spatial resolution has been studied with full GEANT simulation to calculate the systematic uncertainty due to multiple scattering. Several cluster position-finding algorithms have been applied for inclined tracks. The cluster profile and spatial resolution have the predicted geometrical correlation to the track angle. (orig.)

[en] Tailoring nanoscale defect structures for desirable deformation behaviors is crucial to designing and optimizing the mechanical properties of alloys. Distinguishing from the predominant toughening mechanisms (e.g., mechanical twinning and deformation-induced phase transformation), here we report an unusual stacking-fault-mediated deformation in equiatomic FeNiCoCr high-entropy alloy (HEA) by controllably introducing helium nanobubbles with high pressures of ~2.5-4.7 gigapascals. Using in situ transmission electron microscopy nanomechanical testing, we demonstrate that highly pressurized helium nanobubbles can not only increase the strength by serving as dislocation obstacles but also enhance the strain hardening capacity and accommodate considerable plasticity via facilitating the multiplication and interaction of interwoven stacking faults. Through atomistic simulations, we reveal that high helium pressures contribute to reducing the nucleation energy of partial dislocations at the nanobubbles surface, which enhances dislocation nucleation rates and offers sustainable stacking fault sources for retaining ductility. Our results provide a novel design strategy for tuning deformation mechanisms of HEAs via introducing highly pressurized helium nanobubbles, which may open up avenues towards the facile tailoring of mechanical responses in micro/nanoscale HEA components.