Laser and 3-Dimensional Printers: Characterizing Emissions and Occupational Exposures

Introduction: Toxicology and epidemiology studies have observed an association between ultrafine particles (UFPs) and respiratory, cardiovascular, and neurological health effects. While there is a paucity of data in the literature on the potential toxicity and health effects from indoor UFP exposure, more exposure assessment studies and research evaluating the efficacy of controls is merited. An increased demand for efficiency, productivity, and manufacturing has led to conception of laser and 3- dimmensional (3-D) printers in various indoor workplaces. The indoor environment is one of the most important determinants of personal exposure. Introducing laser and 3-D printers to indoor workplaces, introduces a potential indoor source of UFP emissions. Given the current knowledge on the potential health effects from exposure to UFPs, Further research is needed to fully characterize occupational exposures to printer emissions and evaluate factors influencing exposures to better guide control strategies. Methods: The source-receptor model was used to identify relevant factors that may affect emissions and worker exposure. Mixed-effects regression modeling was used to identify sources of variability in exposure to laser printer emissions. UFP and copollutant emissions from laser printers were measured in a laboratory chamber to test the hypothesis that device-specific factors (e.g. make-model, technology, print speed, voltage) influence printer emission profiles. Results are described in Chapter 2. Realtime air samples for UFPs were collected at a laser printing facility. Emission rates for laboratory and real-world exposures were calculated using a one-box model and compared to emission rates calculated using the test method for hard copy devices to determine if results were significantly different. Results are described in Chapter 3. Real-time and time-integrated personal and area air sampling was performed to characterize indoor UFP and co-pollutant exposures to 3-D printer emissions during industrial printing. Personal and area air levels were characterized during industrial 3-D printing and post-processing tasks to determine if exposures were above occupational exposure limits. Results are described in Chapter 4. Conclusions: Device-specific factors such as, copy rate and printer voltage affect exposure. Laser printers evaluated in this study had higher between-device variance. Control strategies should focus on device-specific factors (e.g. copy rate). Future research will focus on other factors potentially influencing exposure (e.g. toner type, paper type). The test method for hard copy devices emission rates differed significantly differed from the one-box model emission rates. Continued research will use exposure and dose modeling to provide estimates and distributions that are meaningful or comparable to previously published data. Occupational exposures to metals and organic vapors during industrial 3-D printing were below respective occupational exposure limits. Further research is needed to fully characterize exposure and understand determinants (e.g. materials, tasks) of higher or lower exposure

Stellar migration and chemical enrichment in the milky way disc: a hybrid model

We develop a hybrid model of galactic chemical evolution that combines a multiring computation of chemical enrichment with a prescription for stellar migration and the vertical distribution of stellar populations informed by a cosmological hydrodynamic disc galaxy simulation. Our fiducial model adopts empirically motivated forms of the star formation law and star formation history, with a gradient in outflow mass loading tuned to reproduce the observed metallicity gradient. With this approach, the model reproduces many of the striking qualitative features of the Milky Way disc’s abundance structure: (i) the dependence of the [O/Fe]–[Fe/H] distribution on radius Rgal and mid-plane distance |z|; (ii) the changing shapes of the [O/H] and [Fe/H] distributions with Rgal and |z|; (iii) a broad distribution of [O/Fe] at sub-solar metallicity and changes in the [O/Fe] distribution with Rgal, |z|, and [Fe/H]; (iv) a tight correlation between [O/Fe] and stellar age for [O/Fe] > 0.1; (v) a population of young and intermediate-age α-enhanced stars caused by migration-induced variability in the Type Ia supernova rate; (vi) non-monotonic age–[O/H] and age–[Fe/H] relations, with large scatter and a median age of ∼4 Gyr near solar metallicity. Observationally motivated models with an enhanced star formation rate ∼2 Gyr ago improve agreement with the observed age–[Fe/H] and age–[O/H] relations, but worsen agreement with the observed age–[O/Fe] relation. None of our models predict an [O/Fe] distribution with the distinct bimodality seen in the observations, suggesting that more dramatic evolutionary pathways are required. All code and tables used for our models are publicly available through the Versatile Integrator for Chemical Evolution (VICE; https://pypi.org/project/vice)

Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68

We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z$_{\odot}$, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M$_{\rm HI}$ $=$ 2.8$\times$10$^{7}$ M$_{\odot}$), recently star-forming (SFR$_{\rm FUV}$ $=$ 1.4$\times$10$^{-3}$ M$_{\odot}$ yr$^{-1}$, SFR$_{\rm H\alpha}$ $<$ 7$\times$10$^{-5}$ M$_{\odot}$ yr$^{-1}$) companion has the same systemic velocity as DDO 68 (V$_{\rm sys}$ $=$ 506 km s$^{-1}$; D $=$ 12.74$\pm$0.27 Mpc) and is located at a projected distance of 42 kpc. New HI maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness HI gas forms a bridge between these objects.Comment: Accepted for publication in the Astrophysical Journal Letter

Natural and Experimental Infection of Caenorhabditis Nematodes by Novel Viruses Related to Nodaviruses

Novel viruses have been discovered in wild Caenorahbditis nematode isolates and can now be used to explore host antiviral pathways, nematode ecology, and host-pathogen co-evolution

Enrichment and characterization of ammonia-oxidizing archaea from the open ocean : phylogeny, physiology and stable isotope fractionation

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 5 (2011): 1796–1808, doi:10.1038/ismej.2011.58.Archaeal genes for ammonia oxidation are widespread in the marine environment, but direct physiological evidence for ammonia oxidation by marine archaea is limited. We report the enrichment and characterization of three strains of pelagic ammonia-oxidizing archaea (AOA) from the north Pacific Ocean that have been maintained in laboratory culture for over three years. Phylogenetic analyses indicate the three strains belong to a previously identified clade of water column-associated AOA and possess 16S rRNA genes and ammonia monooxygenase subunit a (amoA) genes highly similar (98-99% identity) to those recovered in DNA and cDNA clone libraries from the open ocean. The strains grow in natural seawater-based liquid medium while stoichiometrically converting ammonium (NH4 +) to nitrite (NO2 -). Ammonia oxidation by the enrichments is only partially inhibited by allylthiourea at concentrations known to inhibit cultivated ammonia-oxidizing bacteria. The three strains were used to determine the nitrogen stable isotope effect (15εNH3) during archaeal ammonia oxidation, an important parameter for interpreting stable isotope ratios in the environment. Archaeal 15εNH3 ranged from 13- 41‰, within the range of that previously reported for ammonia-oxidizing bacteria. Despite low amino acid identity between the archaeal and bacterial Amo proteins, their functional diversity as captured by 15εNH3 is similar.This work was supported by a Woods Hole Oceanographic Institution (WHOI) Postdoctoral Scholar fellowship to AES and the WHOI Ocean Life Institute

A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT

Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign

In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109Me. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.http://iopscience.iop.org/2041-8205am2022Physic