227 research outputs found

    PassNote: A Feedback Tool for Improving Student Success Outcomes

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    When Purdue University faculty asked for assistance in composing feedback messages to students, Information Technology at Purdue (ITaP) developed PassNote, a feedback tool that integrates good practice into the process of providing formative assessments. PassNote gives faculty customizable feedback prompts (snippets) and lets them connect students with information and links to services such as tutoring,Supplemental Instruction, library resources, technology tools, and workshops. PassNote message starters are often incomplete, allowing instructors to include course-specific information such as office hours and departmental resources

    230 GHz VLBI OBSERVATIONS OF M87: EVENT‐HORIZON‐SCALE STRUCTURE DURING AN ENHANCED VERY‐HIGH‐ENERGY γ‐RAY STATE IN 2012

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    We report on 230 GHz (1.3 mm) very long baseline interferometry (VLBI) observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona, and Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI interferometric phase information on M87 through measurement of the closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0° as expected by physically motivated models for 230 GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ~1 X 10[superscript 10] K derived from the compact flux density of ~1 Jy and the angular size of ~40 µas ~ 5.5 R[subscript s], which is broadly consistent with the peak brightness of the radio cores at 1–86 GHz located within ~10[superscript 2] R[subscript s]. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) γ-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ~20–60 R[subscript s]

    Superresolution Full-polarimetric Imaging for Radio Interferometry with Sparse Modeling

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    We propose a new technique for radio interferometry to obtain superresolution full-polarization images in all four Stokes parameters using sparse modeling. The proposed technique reconstructs the image in each Stokes parameter from the corresponding full-complex Stokes visibilities by utilizing two regularization functions: the ℓ 1 norm and the total variation (TV) of the brightness distribution. As an application of this technique, we present simulated linear polarization observations of two physically motivated models of M87 with the Event Horizon Telescope. We confirm that ℓ 1+TV regularization can achieve an optimal resolution of ~25%–30% of the diffraction limit λ/D[subscript max], which is the nominal spatial resolution of a radio interferometer for both the total intensity (i.e., Stokes I) and linear polarizations (i.e., Stokes Q and U). This optimal resolution is better than that obtained from the widely used Cotton–Schwab CLEAN algorithm or from using ℓ 1 or TV regularizations alone. Furthermore, we find that ℓ 1+TV regularization can achieve much better image fidelity in linear polarization than other techniques over a wide range of spatial scales, not only in the superresolution regime, but also on scales larger than the diffraction limit. Our results clearly demonstrate that sparse reconstruction is a useful choice for high-fidelity full-polarimetric interferometric imaging

    1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales

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    Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic Center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*.Comment: 8 pages, submitted to ApJ

    MicroRNA Regulation of Cell Lineages in Mouse and Human Embryonic Stem Cells

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    SummaryCell fate decisions of pluripotent embryonic stem (ES) cells are dictated by activation and repression of lineage-specific genes. Numerous signaling and transcriptional networks progressively narrow and specify the potential of ES cells. Whether specific microRNAs help refine and limit gene expression and, thereby, could be used to manipulate ES cell differentiation has largely been unexplored. Here, we show that two serum response factor (SRF)-dependent muscle-specific microRNAs, miR-1 and miR-133, promote mesoderm formation from ES cells but have opposing functions during further differentiation into cardiac muscle progenitors. Furthermore, miR-1 and miR-133 were potent repressors of nonmuscle gene expression and cell fate during mouse and human ES cell differentiation. miR-1's effects were in part mediated by translational repression of the Notch ligand Delta-like 1 (Dll-1). Our findings indicate that muscle-specific miRNAs reinforce the silencing of nonmuscle genes during cell lineage commitment and suggest that miRNAs may have general utility in regulating cell-fate decisions from pluripotent ES cells

    Imaging the Schwarzschild-radius-scale Structure of M87 with the Event Horizon Telescope Using Sparse Modeling

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    We propose a new imaging technique for radio and optical/infrared interferometry. The proposed technique reconstructs the image from the visibility amplitude and closure phase, which are standard data products of short-millimeter very long baseline interferometers such as the Event Horizon Telescope (EHT) and optical/infrared interferometers, by utilizing two regularization functions: the ℓ_1-norm and total variation (TV) of the brightness distribution. In the proposed method, optimal regularization parameters, which represent the sparseness and effective spatial resolution of the image, are derived from data themselves using cross-validation (CV). As an application of this technique, we present simulated observations of M87 with the EHT based on four physically motivated models. We confirm that ℓ_1 + TV regularization can achieve an optimal resolution of ~20%–30% of the diffraction limit λ/D_(max), which is the nominal spatial resolution of a radio interferometer. With the proposed technique, the EHT can robustly and reasonably achieve super-resolution sufficient to clearly resolve the black hole shadow. These results make it promising for the EHT to provide an unprecedented view of the event-horizon-scale structure in the vicinity of the supermassive black hole in M87 and also the Galactic center Sgr A*
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