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Controlling attosecond angular streaking with second harmonic radiation.
Hammond, T J,Kim, Kyung Taec,Zhang, Chunmei,Villeneuve, D M,Corkum, P B Optical Society of America 2015 Optics letters Vol.40 No.8
<P>High harmonic generation, which produces a coherent burst of radiation every half cycle of the driving field, has been combined with ultrafast wavefront rotation to create a series of spatially separated attosecond pulses, called the attosecond lighthouse. By adding a coherent second harmonic beam with polarization parallel to the fundamental, we decrease the generating frequency from twice per optical cycle to once. The increased temporal separation increases the pulse contrast. By scanning the carrier envelope phase, we see that the signal is 2π periodic.</P>
Attosecond pulses measured from the attosecond lighthouse
Hammond, T. J.,Brown, Graham G.,Kim, Kyung Taec,Villeneuve, D. M.,Corkum, P. B. Nature Publishing Group, a division of Macmillan P 2016 Nature photonics Vol.10 No.3
<P>The attosecond lighthouse is a method of using ultrafast wavefront rotation with high-harmonic generation to create a series of coherent, spatially separated attosecond pulses. Previously, temporal measurements by photoelectron streaking characterized isolated attosecond pulses created by manipulating the single-atom response(1-4). The attosecond lighthouse, in contrast, generates a series of pulses that spatially separate and become isolated by propagation. Here, we show that ultrafast wavefront rotation maintains the single-atom response (in terms of temporal character) of an isolated attosecond pulse over two octaves of bandwidth. Moreover, we exploit the unique property of the attosecond lighthouse-the generation of several isolated pulses-to measure the three most intense pulses. These pulses each have a unique spectrum and spectral phase.</P>
Han, J. Y.,Chung, J.,Kim, J.,Seo, E. Y.,Kilcrease, J. P.,Bauchan, G. R.,Lim, S.,Hammond, J.,Lim, H. S. Springer Science + Business Media 2016 Virus genes Vol.52 No.4
<P>In 2014, we performed a nationwide survey in Korean radish fields to investigate the distribution and variability of Turnip mosaic virus (TuMV). Brassica rapa ssp. pekinensis sap-inoculated with three isolates of TuMV from infected radish tissue showed different symptom severities, whereas symptoms in Raphanus sativus were similar for each isolate. The helper component-protease (HC-Pro) genes of each isolate were sequenced, and phylogenetic analysis showed that the three Korean isolates were clustered into the basal-BR group. The HC-Pro proteins of these isolates were tested for their RNA silencing suppressor (VSR) activity and subcellular localization in Nicotiana benthamiana. A VSR assay by co-agroinfiltration of HC-Pro with soluble-modified GFP (smGFP) showed that HC-Pro of isolate R007 and R041 showed stronger VSR activity than R065. The HC-Pros showed 98.25 % amino acid identity, and weak VSR isolate (R065) has a single variant residue in the C-terminal domain associated with protease activity and self-interaction compared to isolates with strong VSR activity. Formation of large subcellular aggregates of GFP: HC-Pro fusion proteins in N. benthamiana was only observed for HC-Pro from isolates with strong VSR activity, suggesting that R065 'weak' HC-Pro may have diminished self-association; substitution of the variant C-terminal residue largely reversed the HC-Pro aggregation and silencing suppressor characteristics. The lack of correlation between VSR efficiency and induction of systemic necrosis (SN) suggests that differences in viral accumulation due to HC-Pro are not responsible for SN.</P>
Park, C. H.,Ju, H. K.,Han, J. Y.,Park, J. S.,Kim, I. H.,Seo, E. Y.,Kim, J. K.,Hammond, J.,Lim, H. S. Springer Science + Business Media 2017 Virus genes Vol.53 No.2
<P>Seed-transmitted viruses have caused significant damage to watermelon crops in Korea in recent years, with cucumber green mottle mosaic virus (CGMMV) infection widespread as a result of infected seed lots. To determine the likely origin of CGMMV infection, we collected CGMMV isolates from watermelon and melon fields and generated full-length infectious cDNA clones. The full-length cDNAs were cloned into newly constructed binary vector pJY, which includes both the 35S and T7 promoters for versatile usage (agroinfiltration and in vitro RNA transcription) and a modified hepatitis delta virus ribozyme sequence to precisely cleave RNA transcripts at the 3' end of the tobamovirus genome. Three CGMMV isolates (OMpj, Wpj, and Mpj) were separately evaluated for infectivity in Nicotiana benthamiana, demonstrated by either Agroinfiltration or inoculation with in vitro RNA transcripts. CGMMV nucleotide identities to other tobamoviruses were calculated from pairwise alignments using DNAMAN. CGMMV identities were 49.89% to tobacco mosaic virus; 49.85% to pepper mild mottle virus; 50.47% to tomato mosaic virus; 60.9% to zucchini green mottle mosaic virus; and 60.96% to kyuri green mottle mosaic virus, confirming that CGMMV is a distinct species most similar to other cucurbit-infecting tobamoviruses. We further performed phylogenetic analysis to determine relationships of our new Korean CGMMV isolates to previously characterized isolates from Canada, China, India, Israel, Japan, Korea, Russia, Spain, and Taiwan available from NCBI. Analysis of CGMMV amino acid sequences showed three major clades, broadly typified as 'Russian,' 'Israeli,' and 'Asian' groups. All of our new Korean isolates fell within the 'Asian' clade. Neither the 128 nor 186 kDa RdRps of the three new isolates showed any detectable gene silencing suppressor function.</P>
Insights Into Emissions and Exposures From Use of Industrial-Scale Additive Manufacturing Machines
Stefaniak, A.B.,Johnson, A.R.,du Preez, S.,Hammond, D.R.,Wells, J.R.,Ham, J.E.,LeBouf, R.F.,Martin, S.B. Jr.,Duling, M.G.,Bowers, L.N.,Knepp, A.K.,de Beer, D.J.,du Plessis, J.L. Occupational Safety and Health Research Institute 2019 Safety and health at work Vol.10 No.2
Background: Emerging reports suggest the potential for adverse health effects from exposure to emissions from some additive manufacturing (AM) processes. There is a paucity of real-world data on emissions from AM machines in industrial workplaces and personal exposures among AM operators. Methods: Airborne particle and organic chemical emissions and personal exposures were characterized using real-time and time-integrated sampling techniques in four manufacturing facilities using industrial-scale material extrusion and material jetting AM processes. Results: Using a condensation nuclei counter, number-based particle emission rates (ERs) (number/min) from material extrusion AM machines ranged from $4.1{\times}10^{10}$ (Ultem filament) to $2.2{\times}10^{11}$ [acrylonitrile butadiene styrene and polycarbonate filaments). For these same machines, total volatile organic compound ERs (${\mu}g/min$) ranged from $1.9{\times}10^4$ (acrylonitrile butadiene styrene and polycarbonate) to $9.4{\times}10^4$ (Ultem). For the material jetting machines, the number-based particle ER was higher when the lid was open ($2.3{\times}10^{10}number/min$) than when the lid was closed ($1.5-5.5{\times}10^9number/min$); total volatile organic compound ERs were similar regardless of the lid position. Low levels of acetone, benzene, toluene, and m,p-xylene were common to both AM processes. Carbonyl compounds were detected; however, none were specifically attributed to the AM processes. Personal exposures to metals (aluminum and iron) and eight volatile organic compounds were all below National Institute for Occupational Safety and Health (NIOSH)-recommended exposure levels. Conclusion: Industrial-scale AM machines using thermoplastics and resins released particles and organic vapors into workplace air. More research is needed to understand factors influencing real-world industrial-scale AM process emissions and exposures.
Insights Into Emissions and Exposures From Use of Industrial-Scale Additive Manufacturing Machines
A.B. Stefaniak,A.R. Johnson,S. du Preez,D.R. Hammond,J.R. Wells,J.E. Ham,R.F. LeBouf,S.B. Martin Jr.,M.G. Duling,L.N. Bowers,A.K. Knepp,D.J. de Beer,J.L. du Plessis 한국산업안전보건공단 산업안전보건연구원 2019 Safety and health at work Vol.10 No.2
Background: Emerging reports suggest the potential for adverse health effects from exposure to emissions from some additive manufacturing (AM) processes. There is a paucity of real-world data on emissions from AM machines in industrial workplaces and personal exposures among AM operators. Methods: Airborne particle and organic chemical emissions and personal exposures were characterized using real-time and time-integrated sampling techniques in four manufacturing facilities using industrial-scale material extrusion and material jetting AM processes. Results: Using a condensation nuclei counter, number-based particle emission rates (ERs) (number/min) from material extrusion AM machines ranged from 4.1 1010 (Ultem filament) to 2.2 1011 [acrylonitrile butadiene styrene and polycarbonate filaments). For these same machines, total volatile organic compound ERs (mg/min) ranged from 1.9 104 (acrylonitrile butadiene styrene and polycarbonate) to 9.4 104 (Ultem). For the material jetting machines, the number-based particle ER was higher when the lid was open (2.3 1010 number/min) than when the lid was closed (1.5e5.5 109 number/min); total volatile organic compound ERs were similar regardless of the lid position. Low levels of acetone, benzene, toluene, and m,p-xylene were common to both AM processes. Carbonyl compounds were detected; however, none were specifically attributed to the AM processes. Personal exposures to metals (aluminum and iron) and eight volatile organic compounds were all below National Institute for Occupational Safety and Health (NIOSH)-recommended exposure levels. Conclusion: Industrial-scale AM machines using thermoplastics and resins released particles and organic vapors into workplace air. More research is needed to understand factors influencing real-world industrial- scale AM process emissions and exposures.