186 research outputs found
Viscosity of Silica and Doped Silica Melts: Evidence for a Crossover Temperature
Silica is known as the archetypal strong liquid, exhibiting an Arrhenius
viscosity curve with a high glass transition temperature and constant
activation energy. However, given the ideally isostatic nature of the silica
network, the presence of even a small concentration of defects can lead to a
significant decrease in both the glass transition temperature and activation
energy for viscous flow. To understand the impact of trace level dopants on the
viscosity of silica, we measure the viscosity-temperature curves for seven
silica glass samples having different impurities, including four natural and
three synthetic samples. Depending on the type of dopant, the glass transition
temperature can vary by nearly 300 K. A common crossover is found for all
viscosity curves around ~2200-2500 K, which we attribute to a change of the
transport mechanism in the melt from being dominated by intrinsic defects at
high temperature to dopant-induced defects at low temperatures
Material-independent crack arrest statistics: Application to indentation experiments
An extensive experimental study of indentation and crack arrest statistics is
presented for four different brittle materials (alumina, silicon carbide,
silicon nitride, glass). Evidence is given that the crack length statistics can
be described by a universal (i.e. material independent) distribution. The
latter directly derives from results obtained when modeling crack propagation
as a depinning phenomenon. Crack arrest (or effective toughness) statistics
appears to be fully characterized by two parameters, namely, an asymptotic
crack length (or macroscopic toughness) value and a power law size dependent
width. The experimental knowledge of the crack arrest statistics at one given
scale thus gives access to its knowledge at all scales
In-beam internal conversion electron spectroscopy with the SPICE detector
The SPectrometer for Internal Conversion Electrons (SPICE) has been
commissioned for use in conjunction with the TIGRESS -ray spectrometer
at TRIUMF's ISAC-II facility. SPICE features a permanent rare-earth magnetic
lens to collect and direct internal conversion electrons emitted from nuclear
reactions to a thick, highly segmented, lithium-drifted silicon detector. This
arrangement, combined with TIGRESS, enables in-beam -ray and internal
conversion electron spectroscopy to be performed with stable and radioactive
ion beams. Technical aspects of the device, capabilities, and initial
performance are presented
Super FSR tunable optical microbubble resonator
An optical resonator is often called fully tunable if its tunable range
exceeds the spectral interval that contains the resonances at all the
characteristic modes of this resonator. For the high Q-factor spheroidal and
toroidal microresonators, this interval coincides with the azimuthal free
spectral range. In this Letter, we demonstrate the first mechanically fully
tunable spheroidal microresonator created of a silica microbubble having a 100
micron order radius and a micron order wall thickness. The tunable bandwidth of
this resonator is more than two times greater than its azimuthal free spectral
range
Neurology
Contains reports on eleven research projects.U.S. Air Force (AF49(638)-1130)Army Chemical Corps (DA-18-108-405-Cml-942)U.S. Public Health Service (B-3055)National Science Foundation (Grant G-16526)U.S. Public Health Service (B-3090)U.S. Air Force (AF33(616)-7588)Office of Naval Research (Nonr-1841(70)
Waveguide-integrated silicon T centres
The performance of modular, networked quantum technologies will be strongly
dependent upon the quality of their quantum light-matter interconnects.
Solid-state colour centres, and in particular T centres in silicon, offer
competitive technological and commercial advantages as the basis for quantum
networking technologies and distributed quantum computing. These newly
rediscovered silicon defects offer direct telecommunications-band photonic
emission, long-lived electron and nuclear spin qubits, and proven native
integration into industry-standard, CMOS-compatible, silicon-on-insulator (SOI)
photonic chips at scale. Here we demonstrate further levels of integration by
characterizing T centre spin ensembles in single-mode waveguides in SOI. In
addition to measuring long spin T_1 times, we report on the integrated centres'
optical properties. We find that the narrow homogeneous linewidth of these
waveguide-integrated emitters is already sufficiently low to predict the future
success of remote spin-entangling protocols with only modest cavity Purcell
enhancements. We show that further improvements may still be possible by
measuring nearly lifetime-limited homogeneous linewidths in isotopically pure
bulk crystals. In each case the measured linewidths are more than an order of
magnitude lower than previously reported and further support the view that
high-performance, large-scale distributed quantum technologies based upon T
centres in silicon may be attainable in the near term
Digital Signal Processing
Contains research objectives and reports on sixteen research projects.U.S. Navy - Office of Naval Research (Contract N00014-75-C-0852)National Science Foundation FellowshipNational Science Foundation (Grant ENG76-24117)U.S. Navy - Office of Naval Research (Contract N00014-77-C-0257)U.S. Air Force (Contract F19628-80-C-0002)U.S. Navy - Office of Naval Research (Contract N00014-75-C-0951)Schlumberger-Doll Research Center FellowshipHertz Foundation FellowshipGovernment of Pakistan ScholarshipU.S. Navy - Office of Naval Research (Contract N00014-77-C-0196
Neurology
Contains research objectives and reports on six research projects.U.S. Public Health Service (B-3055)U.S. Public Health Service (B-3090)Office of Naval Research (Nonr-1841 (70))Air Force (AF33(616)-7588)Air Force (AFAFOSR-155-63)Air Force (AFAFOSR-155-63)Army Chemical Corps (DA-18-108-405-Cml-942)National Science Foundation (Grant G-16526
Digital Signal Processing
Contains a research summary and reports on fifteen research projects.National Science Foundation FellowshipJoint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant ENG76-24117)U.S. Navy - Office of Naval Research (Contract N00014-75-C-0951)National Science Foundation (Grant ENG76-24117)Schlumberger-Doll Research Center FellowshipHertz Foundation FellowshipNational Aeronautics and Space Administration (Grant NSG-5157)U.S. Navy - Office of Naval Research (Contract N00014-77-C-0196
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