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

Concurrent 43 and 86 GHz Very Long Baseline Polarimetry of 3C273

We present sub-milliarcsecond resolution total intensity and linear polarization VLBI images of 3C273, using concurrent 43 and 86 GHz data taken with the Very Long Baseline Array in May 2002. The structure seen in the innermost jet suggest that we have fortuitously caught the jet in the act of changing direction. The polarization images confirm that the core is unpolarized (fractional polarization m < 1 %) at 86 GHz, but also show well ordered magnetic fields (m ~ 15 %) in the inner jet, at a projected distance of 2.3 pc from the core. In this strongly polarized region, the rotation measure changes across the jet by 4.2 x 10^{4} rad m^{-2} over an angular width of about 0.3 milliarcseconds. If the lack of polarization in the core is also attributed to a Faraday screen, then a rotation measure dispersion > 5.2 x 10^{4} rad m^{-2} must be present in or in front of that region. These are among the highest rotation measures reported so far in the nucleus of any active galaxy or quasar, and must occur outside (but probably close to) the radio emitting region. The transverse rotation measure gradient is in the same sense as that observed by Asada et al and by Zavala and Taylor at greater core distances. The magnitude of the transverse gradient decreases rapidly with distance down the jet, and appears to be variable.Comment: 4 pages, LaTeX, 3 postscript figures, submitted to Astrophysical Journal Letter

Inconsistency in 9 mm bullets : correlation of jacket thickness to post-impact geometry measured with non-destructive X-ray computed tomography

Fundamental to any ballistic armour standard is the reference projectile to be defeated. Typically, for certification purposes, a consistent and symmetrical bullet geometry is assumed, however variations in bullet jacket dimensions can have far reaching consequences. Traditionally, characteristics and internal dimensions have been analysed by physically sectioning bullets – an approach which is of restricted scope and which precludes subsequent ballistic assessment. The use of a non-destructive X-ray computed tomography (CT) method has been demonstrated and validated Kumar et al., 2011); the authors now apply this technique to correlate bullet impact response with jacket thickness variations. A set of 20 bullets (9 mm DM11) were selected for comparison and an image-based analysis method was employed to map jacket thickness and determine the centre of gravity of each specimen. Both intra- and inter-bullet variations were investigated, with thickness variations of the order of 200 um commonly found along the length of all bullets and angular variations of up to 50 um in some. The bullets were subsequently impacted against a rigid flat plate under controlled conditions (observed on a high-speed video camera) and the resulting deformed projectiles were re-analysed. The results of the experiments demonstrate a marked difference in ballistic performance between bullets from different manufacturers and an asymmetric thinning of the jacket is observed in regions of pre-impact weakness. The conclusions are relevant for future soft armour standards and provide important quantitative data for numerical model correlation and development. The implications of the findings of the work on the reliability and repeatability of the industry standard V50 ballistic test are also discussed

Radio Jet-Ambient Medium Interactions on Parsec Scales in the Blazar 1055+018

As part of our study of the magnetic fields of AGN we have recently observed a large sample of blazars with the Very Long Baseline Array. Here we report the discovery of a striking two-component jet in the source 1055+018, consisting of an inner spine with a transverse magnetic field, and a fragmentary but distinct boundary layer with a longitudinal magnetic field. The polarization distribution in the spine strongly supports shocked-jet models while that in the boundary layer suggests interaction with the surrounding medium. This behavior suggests a new way to understand the differing polarization properties of strong- and weak-lined blazars.Comment: LaTex; 10 pages; 6 figures; reference fix; to appear in ApJL, 518, 1999 June 2

Designing surveys to investigate the impacts of wildfire smoke on human health

Wildfires are increasing in frequency. One area of research interest centers on the pollutants within wildfire smoke, including but not limited to particulate matter and polycyclic aromatic hydrocarbons. These chemicals are associated with exacerbation of respiratory, cardiovascular, dermatological, reproductive, oncological, gastrointestinal, and infectious conditions. As wildfires becoming increasingly prevalent, it will be important for researchers and clinicians to have access to surveillance tools that allow insight into how wildfire smoke exposure is affecting the health of certain populations. We developed a survey tool to characterize exposure to wildfire smoke and subsequent self-reported health outcomes. I first conducted a literature search to identify known and potential negative health outcomes associated with exposure to wildfire smoke. I found a total of 24 articles assessing a total of eight outcomes (cardiac, respiratory, dermatologic, gastrointestinal [GI], oncologic, gestational, COVID-19, and influenza). I used this information to conduct a literature search for survey tools. I used 10 surveys of eight outcomes (cardiac, COPD, asthma, smoking status, dermatological, GI, gestational, and recent infection) to develop a novel surveillance tool. The tool has 11 modules, 142 questions and is anticipated to take 40 minutes on average when self-administered.Keywords: wildfire, pollution, PM2.5, PM10, PAH, surve

X-ray computed tomography (XCT) and chemical analysis (EDX and XRF) used in conjunction for cultural conservation: the case of the earliest scientifically described dinosaur Megalosaurus bucklandii

This paper demonstrates the combined use of X-ray computed tomography (XCT), energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescence (XRF) to evaluate the conservational history of the dentary (lower jaw) of Megalosaurus bucklandii Mantell, 1827, the first scientifically described dinosaur. Previous analysis using XCT revealed that the specimen had undergone at least two phases of repair using two different kinds of plaster, although their composition remained undetermined. Additional chemical analysis using EDX and XRF has allowed the determination of the composition of these unidentified plasters, revealing that they are of similar composition, composed dominantly of ‘plaster of Paris’ mixed with quartz sand and calcite, potentially from the matrix material of the Stonesfield Slate, with the trace presence of chlorine. One of the plasters unusually contains the pigment minium (naturally occurring lead tetroxide; Pb22+Pb4+O4) whilst the other seems to have an additional coating of barium hydroxide (Ba(OH)2), indicating that these likely represent two separate stages of repair. The potential of this combined approach for evaluating problematic museum objects for conservation is further discussed as is its usage in cultural heritage today

Utilizing x-ray computed tomography for heritage conservation : the case of megalosaurus bucklandii

Of key importance to any cultural institution is the practice of conservation, the method by which specimens at risk of severe degradation or destruction are treated to ensure that they survive into the future. However, surface inspection is often insufficient to properly inform conservators of the best treatment approach, and where there is little to no record of the conservational history of an object it can be difficult to identify exactly what form of conservation has been undertaken. X-Ray Computed Tomography (XCT) grants a way to overcome these issues by allowing conservators to non-destructively investigate the subsurface details of an artefact to provide essential information on condition of a specimen. Here, the potential of this approach is demonstrated using the first XCT scans of the iconic dentary of Megalosaurus bucklandii Mantell, 1827 (1); the first dinosaur ever named and described scientifically. XCT analysis reveals that the degree of repair is less extensive than previously thought and also elucidates two different material types, M1 and M2, thought to be representative of at least two phases of repair. Finally the potential of this approach is further explored, highlighting its importance for conservation practice, identifying forgeries and hoaxes in addition to potential applications in public engagement

Circular polarization measurement in millimeter-wavelength spectral-line VLBI observations

This paper considers the problem of accurate measurement of circular polarization in imaging spectral-line VLBI observations in the lambda=7 mm and lambda=3 mm wavelength bands. This capability is especially valuable for the full observational study of compact, polarized SiO maser components in the near-circumstellar environment of late-type, evolved stars. Circular VLBI polarimetry provides important constraints on SiO maser astrophysics, including the theory of polarized maser emission transport, and on the strength and distribution of the stellar magnetic field and its dynamical role in this critical circumstellar region. We perform an analysis here of the data model containing the instrumental factors that limit the accuracy of circular polarization measurements in such observations, and present a corresponding data reduction algorithm for their correction. The algorithm is an enhancement of existing spectral line VLBI polarimetry methods using autocorrelation data for calibration, but with innovations in bandpass determination, autocorrelation polarization self-calibration, and general optimizations for the case of low SNR, as applicable at these wavelengths. We present an example data reduction at $\lambda=7$ mm and derive an estimate of the predicted accuracy of the method of m_c < 0.5% or better at lambda=7 mm and m_c < 0.5-1% or better at lambda=3 mm. Both the strengths and weaknesses of the proposed algorithm are discussed, along with suggestions for future work.Comment: 23 pages, 13 figure