38,814 research outputs found

    CS J = 2 yields 1 emission toward the central region of M82

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    M82 is an irregular (Type II) galaxy located at a distance of approximately 3.5 Mpc. Its unusual appearance and high luminosity, particularly in the infrared, has led many astronomers to classify it as a starburst galaxy. This interpretation is supported by the observation of a large number of radio continuum sources within the central arcminute of the galaxy. These sources are thought to be associated with supernova remnants. The starburst in the central region of the galaxy is believed to have been triggered by tidal interaction with either M81 or the HI cloud surrounding the M81 group. High angular resolution CO-12 J=1 to 0 maps by Nakai (1984) and Lo et al. (1987) indicate the existence of a 400 to 450 pc rotating ring of molecular material about the central region of M82. Red- and blue-shifted absorption components of the HI and OH lines measured by Weliachew et al. (1984) provided the first evidence for the presence of the ring. Many astronomers, each using a different angular resolution, have compared CO-12 J=1 to 0, J=2 to 1, and J=3 to 2 emission and concluded that a large fraction of the CO emission is optically thin. Additional observations suggest that the molecular material toward the center of M82 is clumpy and dense. Unlike the lower rotational transitions of CO, CS is excited only at relatively high densities, n sub H sub 2 greater than or equal to 10(exp 4) cm(-3). It is in clouds with these densities that stars are expected to form. This makes CS an excellent probe of star formation regions. Researchers observed the CS J=2 to 1 transition (97.981 GHz) toward 52 positions in M82 using the National Radio Astronomy Observatory (NRAO) 12 m telescope

    ILC Operating Scenarios

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    The ILC Technical Design Report documents the design for the construction of a linear collider which can be operated at energies up to 500 GeV. This report summarizes the outcome of a study of possible running scenarios, including a realistic estimate of the real time accumulation of integrated luminosity based on ramp-up and upgrade processes. The evolution of the physics outcomes is emphasized, including running initially at 500 GeV, then at 350 GeV and 250 GeV. The running scenarios have been chosen to optimize the Higgs precision measurements and top physics while searching for evidence for signals beyond the standard model, including dark matter. In addition to the certain precision physics on the Higgs and top that is the main focus of this study, there are scientific motivations that indicate the possibility for discoveries of new particles in the upcoming operations of the LHC or the early operation of the ILC. Follow-up studies of such discoveries could alter the plan for the centre-of-mass collision energy of the ILC and expand the scientific impact of the ILC physics program. It is envisioned that a decision on a possible energy upgrade would be taken near the end of the twenty year period considered in this report

    Growth of Epitaxial Oxide Thin Films on Graphene

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    The transfer process of graphene onto the surface of oxide substrates is well known. However, for many devices, we require high quality oxide thin films on the surface of graphene. This step is not understood. It is not clear why the oxide should adopt the epitaxy of the underlying oxide layer when it is deposited on graphene where there is no lattice match. To date there has been no explanation or suggestion of mechanisms which clarify this step. Here we show a mechanism, supported by first principles simulation and structural characterisation results, for the growth of oxide thin films on graphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a graphene and show that local defects in the graphene layer (e.g. grain boundaries) act as bridgepillar spots that enable the epitaxial growth of STO thin films on the surface of the graphene layer. This study, and in particular the suggestion of a mechanism for epitaxial growth of oxides on graphene, offers new directions to exploit the development of oxide/graphene multilayer structures and devices

    Neutrino degeneracy and cosmological nucleosynthesis, revisited

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    A reexamination of the effects of non-zero degeneracies on Big Bang Nucleosynthesis is made. As previously noted, non-trivial alterations of the standard model conclusions can be induced only if excess lepton numbers L sub i, comparable to photon number densities eta sub tau, are assumed (where eta sub tau is approx. 3 times 10(exp 9) eta sub b). Furthermore, the required lepton number densities (L sub i eta sub tau) must be different for upsilon sub e than for upsilon sub mu and epsilon sub tau. It is shown that this loophole in the standard model of nucleosynthesis is robust and will not vanish as abundance and reaction rate determinations improve. However, it is also argued that theoretically (L sub e) approx. (L sub mu) approx. (L sub tau) approx. eta sub b is much less than eta sub tau which would preclude this loophole in standard unified models
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