High visibility two photon interference of frequency time entangled photons generated in a quasi phase matched AlGaAs waveguide

We demonstrate experimentally the frequency time entanglement of photon pairs produced in a CW pumped quasi phased matched AlGaAs superlattice waveguide. A visibility of 96.0+-0.7% without background subtraction has been achieved, which corresponds the violation of Bell inequality by 52 standard deviations

Fluorescence Visualization of Newly Synthesized Proteins in Mammalian Cells

Modern proteomic methods enable efficient identification of the hundreds or thousands of proteins present in whole cells or in isolated organelles. However, a thorough understanding of the proteome requires insight into protein localization as well as protein identity. Recently, visualization of newly synthesized proteins in bacterial cells was demonstrated through co-translational introduction of an alkynyl amino acid followed by selective CuI-catalyzed ligation of the alkynyl side chain to the fluorogenic dye 3-azido-7-hydroxycoumarin. Here we report that selective fluorescence labeling and imaging of newly synthesized proteins can be accomplished in a diverse set of mammalian cells

Interstellar Scintillation of the Polarized Flux Density in Quasar, PKS 0405-385

The remarkable rapid variations in radio flux density and polarization of the quasar PKS 0405-385 observed in 1996 are subject to a correlation analysis, from which characteristic time scales and amplitudes are derived. The variations are interpreted as interstellar scintillations. The cm wavelength observations are in the weak scintillation regime for which models for the various auto- and cross-correlations of the Stokes parameters are derived and fitted to the observations. These are well modelled by interstellar scintillation (ISS) of a 30 by 22 micro-as source, with about 180 degree rotation of the polarization angle along its long dimension. This success in explaining the remarkable intra-day variations (IDV)in polarization confirms that ISS gives rise to the IDV in this quasar. However, the fit requires the scintillations to be occurring much closer to the Earth than expected according to the standard model for the ionized interstellar medium (IISM). Scattering at distances in the range 3-30 parsec are required to explain the observations. The associated source model has a peak brightness temperature near 2.0 10^{13}K, which is about twenty-five times smaller than previously derived for this source. This reduces the implied Doppler factor in the relativistic jet, presumed responsible to 10-20, high but just compatible with cm wavelength VLBI estimates for the Doppler factors in Active Galactic Nuclei (AGNs).Comment: 43 pages 15 figures, accepted for ApJ Dec 200

Sterile neutrinos and supernova nucleosynthesis

A light sterile neutrino species has been introduced to explain simultaneously the solar and atmospheric neutrino puzzles and the results of the LSND experiment, while providing for a hot component of dark matter. Employing this scheme of neutrino masses and mixings, we show how matter-enhanced active-sterile neutrino transformation followed by active-active neutrino transformation can solve robustly the neutron deficit problem encountered by models of r-process nucleosynthesis associated with neutrino-heated supernova ejecta.Comment: 29 pages, 3 postscript figures, submitted to Phys. Rev.

Shape of the Galactic Orbits in the CNOC1 Clusters

We present an analysis of the orbital properties in 9 intermediate-redshifts cluster of the CNOC1 survey and we compare them to a control sample of 12 nearby clusters. Similar to the nearby elliptical galaxies, the bulge-dominated galaxies in clusters at redshifts ~0.1-0.4 present orbits that are more eccentric than those for disk-dominated galaxies. However, the orbital segregation is less significant than that found for elliptical and spiral galaxies in nearby cluster. When galaxies are separated by colors - red galaxies with colors in the rest frame (U-V)_o > 1.4, and blue galaxies with (U-V)_o =< 1.4 - the strongest orbital segregation is found. Therefore, the segregation we found seems to modify more efficiently the star formation activity than the internal shape of the galaxies. When we compare the orbits of early-type galaxies at intermediate-redshift with those for z=0, they seem to develop significant changes getting much more eccentric. A different behavior is observed in the late-type galaxies, which present no-significant evolution in their orbit shapes.Comment: Accepted for publication in ApJ, April 2000. Latex with aaspp4.sty, 20 pages, 4 tables, 6 eps figure

1, 2-Bis (phenylsulfonyl)-1H-Indole as an Acceptor of Organocuprate Nucleophiles

1,2-Bis(phenylsulfonyl)-1H-indole is a novel example of an electron-deficient indole that undergoes nucleophilic attack at C-3. Though a variety of other organometallic nucleophiles fail to engender nucleophilic substitution, organocuprates produce 3-substituted 2-(phenylsulfonyl)-1H-indoles. These reactions contribute to the growing number of examples of nucleophilic addition to the indole core

Researching for better instructional methods using AB experiments in MOOCs: results and challenges

We conducted two AB experiments (treatment vs. control) in a massive open online course. The first experiment evaluates deliberate practice activities (DPAs) for developing problem solving expertise as measured by traditional physics problems. We find that a more interactive drag-and-drop format of DPA generates quicker learning than a multiple choice format but DPAs do not improve performance on solving traditional physics problems more than normal homework practice. The second experiment shows that a different video shooting setting can improve the fluency of the instructor which in turn improves the engagement of the students although it has no significant impact on the learning outcomes. These two cases demonstrate the potential of MOOC AB experiments as an open-ended research tool but also reveal limitations. We discuss the three most important challenges: wide student distribution, “open-book” nature of assessments, and large quantity and variety of data. We suggest possible methods to cope with those.Google (Firm)Massachusetts Institute of Technolog

Cryo-EM structure of the Rhodospirillum rubrum RC-LH1 complex at 2.5 Å.

The reaction centre light-harvesting 1 (RC-LH1) complex is the core functional component of bacterial photosynthesis. We determined the cryo-electron microscopy (cryo-EM) structure of the RC-LH1 complex from Rhodospirillum rubrum at 2.5 Å resolution, which reveals a unique monomeric bacteriochlorophyll with a phospholipid ligand in the gap between the RC and LH1 complexes. The LH1 complex comprises a circular array of 16 αβ-polypeptide subunits that completely surrounds the RC, with a preferential binding site for a quinone, designated QP, on the inner face of the encircling LH1 complex. Quinols, initially generated at the RC QB site, are proposed to transiently occupy the QP site prior to traversing the LH1 barrier and diffusing to the cytochrome bc1 complex. Thus, the QP site, which is analogous to other such sites in recent cryo-EM structures of RC-LH1 complexes, likely reflects a general mechanism for exporting quinols from the RC-LH1 complex

Chaotic Amplification of Neutrino Chemical Potentials by Neutrino Oscillations in Big Bang Nucleosynthesis

We investigate in detail the parameter space of active-sterile neutrino oscillations that amplifies neutrino chemical potentials at the epoch of Big Bang Nucleosynthesis. We calculate the magnitude of the amplification and show evidences of chaos in the amplification process. We also discuss the implications of the neutrino chemical potential amplification in the Big Bang Nucleosynthesis. It is shown that with a $\sim 1$ eV \nue, the amplification of its chemical potential by active-sterile neutrino oscillations can lower the effective number of neutrino species at Big Bang Nucleosynthesis to significantly below 3.Comment: Revtex 20 pages, 7 postscript figures. Also by ftp://astro.queensu.ca/pub/shi/ . Submitted to PR