XXVII. Some Coins of the Maukharis, and of the Thanesar Line

n/

A novel method for the injection and manipulation of magnetic charge states in nanostructures

Realising the promise of next-generation magnetic nanotechnologies is contingent on the development of novel methods for controlling magnetic states at the nanoscale. There is currently demand for simple and flexible techniques to access exotic magnetisation states without convoluted fabrication and application processes. 360 degree domain walls (metastable twists in magnetisation separating two domains with parallel magnetisation) are one such state, which is currently of great interest in data storage and magnonics. Here, we demonstrate a straightforward and powerful process whereby a moving magnetic charge, provided experimentally by a magnetic force microscope tip, can write and manipulate magnetic charge states in ferromagnetic nanowires. The method is applicable to a wide range of nanowire architectures with considerable benefits over existing techniques. We confirm the method's efficacy via the injection and spatial manipulation of 360 degree domain walls in Py and Co nanowires. Experimental results are supported by micromagnetic simulations of the tip-nanowire interaction.Comment: in Scientific Reports (2016

86 GHz Very Long Baseline Polarimetry of 3C273 and 3C279 with the Coordinated Millimeter VLBI Array

86 GHz Very Long Baseline Polarimetry probes magnetic field structures within the cores of Active Galactic Nuclei at higher angular resolutions and a spectral octave higher than previously achievable. Observations of 3C273 and 3C279 taken in April 2000 with the Coordinated Millimeter VLBI Array have resulted in the first total intensity (Stokes I) and linear polarization VLBI images reported of any source at 86 GHz. These results reveal the 86 GHz electric vector position angles within the jets of 3C273 and 3C279 to be orthogonal to each other, and the core of 3C273 to be unpolarized. If this lack of polarization is due to Faraday depolarization alone, the dispersion in rotation measure is >=90000 rad/m^2 for the core of 3C273.Comment: AASTeX v5.02; 10 pages; 4 figures; accepted for publication in the Astrophysical Journal Letter

Wavelet-based Faraday Rotation Measure Synthesis

Faraday Rotation Measure (RM) Synthesis, as a method for analyzing multi-channel observations of polarized radio emission to investigate galactic magnetic fields structures, requires the definition of complex polarized intensity in the range of the negative lambda square. We introduce a simple method for continuation of the observed complex polarized intensity into this domain using symmetry arguments. The method is suggested in context of magnetic field recognition in galactic disks where the magnetic field is supposed to have a maximum in the equatorial plane. The method is quite simple when applied to a single Faraday-rotating structure on the line of sight. Recognition of several structures on the same line of sight requires a more sophisticated technique. We also introduce a wavelet-based algorithm which allows us to consider a set of isolated structures. The method essentially improves the possibilities for reconstruction of complicated Faraday structures using the capabilities of modern radio telescopes.Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letter

Performance of Climate Projections for Yukon and Adjacent Northwest Territories, 1991 – 2020

Permafrost foundation design recognizes the impact of climate change on soil bearing capacity, as described in Canadian guideline CSA PLUS 4011:19. There is, however, no guidance as to the climate scenarios most prudent to adopt for such design. We have compared climate change scenarios outlined in 2003 for the design of the proposed Mackenzie Gas Project (MGP) with climate data for 1991 – 2020 to determine the projections most representative of what did, in fact, occur. In Canada, the greatest change in climate during the last 50 years has been measured in the western Arctic, where fluctuations in annual air temperatures are regionally consistent. In this region, the rate of change in annual mean air temperature for 1971 – 2020 has ranged from 0.77 °C decade-1 at Inuvik, NT, to 0.30 °C decade-1 at Komakuk Beach, YT, with warming concentrated in winter. No statistically significant trends in total annual precipitation have been observed and these records are poorly correlated within the region. In 2003, 29 climate projections from seven global climate models were examined for the MGP and, in 2005, for research regarding forest fires in Yukon. The observed climate warming in Yukon and adjacent Northwest Territories during 1991 – 2020 was close to the upper projections for mean annual and winter air temperature. For example, at Inuvik the 2.3 °C increase observed in mean annual air temperature between 1961 – 90 and 1991 – 2020, exceeds the median projection for change by 2010 – 39 of +1.6 °C and approaches the upper value of +2.4 °C. No consistency between observed and projected precipitation has been determined. These results indicate that, when required, future projections of temperature in northwest Canada may prudently adopt higher or more extreme scenarios because they have been the most realistic to date. They imply that near-surface permafrost may soon become unsustainable in southern parts of the region and so site investi gations to locate thaw-stable soils will likely be cost effective for new projects

The COINS Sample - VLBA Identifications of Compact Symmetric Objects

We present results of multifrequency polarimetric VLBA observations of 34 compact radio sources. The observations are part of a large survey undertaken to identify CSOs Observed in the Northern Sky (COINS). Compact Symmetric Objects (CSOs) are of particular interest in the study of the physics and evolution of active galaxies. Based on VLBI continuum surveys of ~2000 compact radio sources, we have defined a sample of 52 CSOs and CSO candidates. In this paper, we identify 18 previously known CSOs, and introduce 33 new CSO candidates. We present continuum images at several frequencies and, where possible, images of the polarized flux density and spectral index distributions for the 33 new candidates and one previously known but unconfirmed source. We find evidence to support the inclusion of 10 of these condidates into the class of CSOs. Thirteen candidates, including the previously unconfirmed source, have been ruled out. Eleven sources require further investigation. The addition of the 10 new confirmed CSOs increases the size of this class of objects by 50%.Comment: 24 pages, incl 8 figures. Accepted for publication in ApJ. Figure quality degraded in the interests of space, full gzipped PS version also available at http://www.ee.nmt.edu/~apeck/papers

Playing Beowulf: Bridging computational thinking, arts and literature through game-making

Preparing younger generations to engage meaningfully with digital technology is often seen as one of the goals of 21st century education. JeanetteWing’s seminal work on Computational Thinking (CT) is an important landmark for this goal: CT represents a way of thinking, a set of problem-solving skills which can be valuable when interacting with digital technologies, and with different fields of knowledge, such as Arts and Humanities. Even if this cross-areas relevance has been celebrated and acknowledged in theoretical research, there has been a lack of practical projects exploring these links between CT and non-STEM fields. This research develops these links. We present a specific case – a game produced by two 14 years-old boys – within Playing Beowulf, a collaboration with the British library’s Young Researchers programme, in which students aged 13–14 from an inner-London (UK) school have developed games based on their own readings of the Anglo-Saxon poem Beowulf during an after-school club. The game was produced using MissionMaker, a software (currently under development at UCL Knowledge Lab) that allows users to create and code their own first-person 3D games in a simple way, using pre-made 3D assets, such as rooms, props, characters and weapons and a simplified programming language manipulated through drop-down lists. We argue that MissionMaker, by simplifying the development process (low floor), can be a means to foster the building of knowledge in both STEM (CT) and Arts and Humanities, building bridges between these two areas inside and outside traditional schooling

Probing the Magnetized Interstellar Medium Surrounding the Planetary Nebula Sh 2-216

We present 1420 MHz polarization images of a 2.5 X 2.5 degree region around the planetary nebula (PN) Sh 2-216. The images are taken from the Canadian Galactic Plane Survey (CGPS). An arc of low polarized intensity appears prominently in the north-east portion of the visible disk of Sh 2-216, coincident with the optically identified interaction region between the PN and the interstellar medium (ISM). The arc contains structural variations down to the ~1 arcminute resolution limit in both polarized intensity and polarization angle. Several polarization-angle "knots" appear along the arc. By comparison of the polarization angles at the centers of the knots and the mean polarization angle outside Sh 2-216, we estimate the rotation measure (RM) through the knots to be -43 +/- 10 rad/m^2. Using this estimate for the RM and an estimate of the electron density in the shell of Sh 2-216, we derive a line-of-sight magnetic field in the interaction region of 5.0 +/- 2.0 microG. We believe it more likely the observed magnetic field is interstellar than stellar, though we cannot completely dismiss the latter possibility. We interpret our observations via a simple model which describes the ISM magnetic field around Sh 2-216, and comment on the potential use of old PNe as probes of the magnetized ISM.Comment: 25 pages, 4 figures. Accepted for publication in the Astrophysical Journa