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STRINGENT LIMITS ON THE POLARIZED SUBMILLIMETER EMISSION FROM PROTOPLANETARY DISKS
Hughes, A. Meredith,Wilner, David J.,Cho, Jungyeon,Marrone, Daniel P.,Lazarian, Alexandre,Andrews, Sean M.,Rao, Ramprasad IOP Publishing 2009 The Astrophysical journal Vol.704 No.2
<P>We present arcsecond-resolution Submillimeter Array (SMA) polarimetric observations of the 880 mu m continuum emission from the protoplanetary disks around two nearby stars, HD 163296 and TW Hydrae. Although previous observations and theoretical work have suggested that a 2%-3% polarization fraction should be common for the millimeter continuum emission from such disks, we detect no polarized continuum emission above a 3 sigma upper limit of 7 mJy in each arcsecond-scale beam, or <1% in integrated continuum emission. We compare the SMA upper limits with the predictions from the exploratory Cho & Lazarian model of polarized emission from T Tauri disks threaded by toroidal magnetic fields, and rule out their fiducial model at the similar to 10 sigma level. We explore some potential causes for this discrepancy, focusing on model parameters that describe the shape, magnetic field alignment, and size distribution of grains in the disk. We also investigate related effects like the magnetic field strength and geometry, scattering off of large grains, and the efficiency of grain alignment, including recent advances in grain alignment theory, which are not considered in the fiducial model. We discuss the impact each parameter would have on the data and determine that the suppression of polarized emission plausibly arises from rounding of large grains, reduced efficiency of grain alignment with the magnetic field, and/or some degree of magnetic field tangling ( perhaps due to turbulence). A poloidal magnetic field geometry could also reduce the polarization signal, particularly for a face-on viewing geometry like the TW Hya disk. The data provided here offer the most stringent limits to-date on the polarized millimeter-wavelength emission from disks around young stars.</P>
Wang Xiao Dong,Gleaves Michael,Meredith David,Allan Rob,Nave Colin The Polymer Society of Korea 2006 Macromolecular Research Vol.14 No.2
E-science refers to the large-scale science that will increasingly be carried out through distributed global collaborations enabled by the Internet. The Grid is a service-oriented architecture proposed to provide access to very large data collections, very large scale computing resources and remote facilities. Web services, which are server applications, enable online access to service providers. Web portal interfaces can further hide the complexity of accessing facility's services. The main use of synchrotron radiation (SR) facilities by protein crystallographers is to collect the best possible diffraction data for reasonably well defined problems. Significant effort is therefore being made throughout the world to automate SR protein crystallography facilities so scientists can achieve high throughput, even if they are not expert in all the techniques. By applying the above technologies, the e-HTPX project, a distributed computing infrastructure, was designed to help scientists remotely plan, initiate and monitor experiments for protein crystallographic structure determination. A description of both the hardware and control software is given together in this paper.