High-Sensitivity 86GHz (3.5mm) VLBI Observations of M87: Deep Imaging of the Jet Base at a 10 Schwarzschild-Radius Resolution

We report on results from new high-sensitivity, high-resolution 86GHz (3.5 millimeter) observations of the jet base in the nearby radio galaxy M87, obtained by the Very Long Baseline Array in conjunction with the Green Bank Telescope. The resulting image has a dynamic range exceeding 1500 to 1, the highest ever achieved for this jet at this frequency, resolving and imaging a detailed jet formation/collimation structure down to ~10 Schwarzschild radii (Rs). The obtained 86GHz image clearly confirms some important jet features known at lower frequencies, i.e., a wide-opening angle jet base, a limb-brightened intensity profile, a parabola-shape collimation profile and a counter jet. The limb-brightened structure is already well developed at < 0.2mas (< 28Rs, projected) from the core, where the corresponding apparent opening angle becomes as wide as ~100 degrees. The subsequent jet collimation near the black hole evolves in a complicated manner; there is a "constricted" structure at tens Rs from the core, where the jet cross section is locally shrinking. We suggest that an external pressure support from the inner part of radiatively-inefficient accretion flow may be dynamically important in shaping/confining the footprint of the magnetized jet. We also present the first VLBI 86GHz polarimetric experiment for this source, where a highly polarized (~20%) feature is detected near the jet base, indicating the presence of a well-ordered magnetic field. As a by-product, we additionally report a 43/86 GHz polarimetric result for our calibrator 3C 273 suggesting an extreme rotation measure near the core.Comment: Accepted for publication in ApJ. 39 pages, 11 figures, 3 table

Monitoring the Galactic Center at 3mm: Study of Flaring of Sagittarius A* and SiO Masers in the Central Parsec

The center of the Milky Way Galaxy is a complex environment, with a super-massive black hole, Sagittarius A* (Sgr A*), at its heart, which is a bright radio source. It undergoes regular bursts of variability, known as flaring. The flaring is also observed in near-IR and X-ray observations. This flaring activity is thought to arise from the innermost region of the accretion flow. One aim of this thesis is to analyze the observations of the Galactic Center at millimeter wavelength to observe and study the flaring activity of Sgr A*. In part these observations were carried out by myself. For this, I have observed the GC at 3 mm wavelength between 2010-2014 with Australia Telescope Compact Array (ATCA). The observations in 2013-2014 were also carried out to study the the flyby of the dusty S-cluster object (DSO/G2) that was supposed to have its periapse passage in 2014, and its effects on the flaring activity of Sgr A*. I obtain the radio light curves of Sgr A* from interferometer data by subtracting the contributions from the surrounding extended emission and correcting the elevation and time dependent gains of the telescope. The observations detect three instances of significant variability in the flux density of Sgr A*, with variations between 0.5 to 1.0 Jy, lasting for 1.5-3 hours. I use the adiabatically expanding plasmon model to analyze the the flux density variations. We derive the physical quantities of the modelled flare emission, which give a source expansion speed of ~ 0.013-0.025c, source sizes of ~ 1-3 Schwarzschild radii, spectral indices of = 0.5-0.8, with the peak of the synchrotron radiation occurring at frequencies of few hundred GHz. These parameters suggest that the expanding source components are either confined to the neighbourhood of Sgr A* by contributing to the corona or the disc, or have a bulk motion greater than the expansion velocity. I do not detect exceptional flux density variation on short flare time-scales during the approach and the flyby of the DSO which is consistent with its observed compactness and the absence of a large bow shock. I also present the observations of SiO maser sources observed in the central parsec of the GC. SgrA* was observed with two intermediate frequencies (IFs) centered at 86.243 GHz and 85.640 GHz corresponding to the two rotational transition lines of the SiO molecule with 2 GHz bandwidth each, and 1 MHz frequency resolution, which corresponds to 3.477 km/s velocity resolution. Our spatial resolution is limited by the available baselines with best resolution of 0.2 arcsec. These are the most comprehensive observations of the central parsec of the GC at 3mm, with wide band that allow us to investigate high velocity stars. In the thesis, I present the method to detect the maser sources. In total, 11 sources were detected, of which 8 are previously known sources, like: IRS 1W, IRS 2L, IRS 7, IRS 9, IRS 10EE, IRS 12N, IRS 28 and IRS 34. Three new sources were detected. I present the method to calculate the accurate positions and proper motions of the maser sources. The proper motions of strong sources IRS 7 & IRS 12N are calculated precisely and are in agreement with previous results. Comparative study of the relative strength of the SiO transition lines indicates that the 86.243 GHz line is stronger than the 85.640 GHz line. Among the detected stars, 3 are cool stars, 2 HE I stars, 1 AGB star and 1 red giant. I also present an upper limit on the detection of several maser sources which have been detected in previous studies but were not detected in my dataset. This is most likely due to the strong variability of the maser emission

NASA Tech Briefs, March 2002

Topics include: a special section on data acquisition, software, electronic components and systems, materials, computer programs, mechanics, machinery/automation, manufacturing, biomedical, physical sciences, book and reports, and a special section of Photonics Tech Briefs

New Calibrator with Points Distributed Conical Helically for Online Calibration of C-Arm

To improve the accuracy of calibration of C-arm, and overcome the space limitation in surgery, we proposed a new calibrator for online calibration of C-arm. After the image rectification by a polynomial fitting-based global correction method, the C-arm was assumed as an ideal pinhole model. The relationships between two kinds of spatial calibration errors and the distribution of fiducial points were studied: the performance of FRE (Fiducial Registration Error) and TRE (Target Registration Error) were not consistent, but both were best at the 12 marked points; the TRE decreased with the increase of the uniformity of calibration points distribution, and with the decrease of the distance between the target point and the center of calibration points. A calibrator with 12 fiducial points conical helically distributed, which could be placed on the knee, was an attractive option. A total of 10 experiments on C-arm calibration accuracy were conducted and the mean value of mapping error was 0.41 mm. We designed an ACL reconstruction navigation system and carried out specimen experiments on 4 pairs of dry femur and tibia. The mean accuracy of navigation system was 0.85 mm, which is important to the tunnel positioning for ACL reconstruction

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

NASA Tech Briefs, November 1992

Topics include: Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome