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Lukens, Katherine E.,Feldstein, Steven B.,Yoo, Changhyun,Lee, Sukyoung Wiley Blackwell (John WileySons) 2017 Quarterly journal of the Royal Meteorological Soci Vol.143 No.703
<P>For all eight MJO phases, it is found that the extratropical response over the North Pacific and North America is almost entirely due to the MJO convection over the western tropical Pacific. The RWS is excited within the first 24 h after the model heating is turned on. For MJO phases 1-3 and 8, the RWS leads to the development of a cyclonic anomaly over southeast Asia via advection of the climatological absolute vorticity by the anomalous divergent wind in the subtropics and by horizontal convergence in the Tropics. MJO phases 4-7 show opposite features. The resulting anomaly is then advected eastward by the climatological zonal wind toward the central Pacific, after which dispersion into the extratropics and the excitation of a Pacific/North American teleconnection pattern takes place.</P>
Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation
Um, Wooyong,Chang, Hyun-Shik,Icenhower, Jonathan P.,Lukens, Wayne W.,Serne, R. Jeffrey,Qafoku, Nikolla P.,Westsik, Joseph H.,Buck, Edgar C.,Smith, Steven C. American Chemical Society 2011 Environmental science & technology Vol.45 No.11
<P>During the nuclear waste vitrification process volatilized <SUP>99</SUP>Tc will be trapped by melter off-gas scrubbers and then washed out into caustic solutions, and plans are currently being contemplated for the disposal of such secondary waste. Solutions containing pertechnetate [<SUP>99</SUP>Tc(VII)O<SUB>4</SUB><SUP>–</SUP>] were mixed with precipitating goethite and dissolved Fe(II) to determine if an iron (oxy)hydroxide-based waste form can reduce Tc(VII) and isolate Tc(IV) from oxygen. The results of these experiments demonstrate that Fe(II) with goethite efficiently catalyzes the reduction of technetium in deionized water and complex solutions that mimic the chemical composition of caustic waste scrubber media. Identification of the phases, goethite + magnetite, was performed using XRD, SEM and TEM methods. Analyses of the Tc-bearing solid products by XAFS indicate that all of the Tc(VII) was reduced to Tc(IV) and that the latter is incorporated into goethite or magnetite as octahedral Tc(IV). Batch dissolution experiments, conducted under ambient oxidizing conditions for more than 180 days, demonstrated a very limited release of Tc to solution (2–7 μg Tc/g solid). Incorporation of Tc(IV) into the goethite lattice thus provides significant advantages for limiting reoxidation and curtailing release of Tc disposed in nuclear waste repositories.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/esthag/2011/esthag.2011.45.issue-11/es104343p/production/images/medium/es-2010-04343p_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/es104343p'>ACS Electronic Supporting Info</A></P>
Effect of Technetium-99 sources on its retention in low activity waste glass
Luksic, Steven A.,Kim, Dong-Sang,Um, Wooyong,Wang, Guohui,Schweiger, Michael J.,Soderquist, Chuck Z.,Lukens, Wayne,Kruger, Albert A. Elsevier 2018 JOURNAL OF NUCLEAR MATERIALS Vol.503 No.-
<P><B>Abstract</B></P> <P>Small-scale crucible melting tests on simulated waste glass were performed with technetium-99 (Tc-99) introduced as different species in a representative low activity waste simulant. The glass saw an increase in Tc-99 retention when TcO<SUB>2</SUB>∙2H<SUB>2</SUB>O and various Tc-minerals containing reduced tetravalent Tc were used compared to tests in which pertechnetate with heptavalent Tc was used. We postulate that the increase of Tc retention is likely caused by different reaction paths for Tc incorporation into glass during early stages of melting, rather than the low volatility of reduced tetravalent Tc compounds, which has been a generally accepted idea. Additional studies are needed to clarify the exact mechanisms relevant to the effect of reduced Tc compounds on Tc incorporation into or volatilization from the glass melt.</P>
Impact of Periampullary Diverticulum on ERCP Performance: A matched Case-Control Study
Juan E. Corral,Omar Y. Mousa,Paul T. Kröner,Victoria Gomez,Frank J. Lukens 대한소화기내시경학회 2019 Clinical Endoscopy Vol.52 No.1
Background/Aims: Periampullary diverticulum (PAD) is frequently encountered during endoscopic retrograde cholangiopancreatography(ERCP) and has been associated with stone formation in the bile duct. The effects of PAD on the ERCP procedure have been oftendebated. We aimed to compare the therapeutic success of ERCP between patients with PAD and matched controls. Methods: We reviewed all ERCPs with findings of PAD in a national database (n=1,089) and compared them with age- and gendermatchedcontrols in a 1:3 fashion (n=3,267). Demographics, endoscopic findings, visualization of main structures, and therapeuticsuccess rates were compared between groups. Secondary analysis compared PAD cases and controls who had gallstone disease. Results: The average cohort age was 68.4±14.3 years and 55.1% were male. ERCP success was similar in both groups, and no significantinter-group differences were found in the multivariate analysis. The presence of PAD did not affect the rates of sphincterotomy orvisualization of main biliary structures. Secondary analysis showed similar success rates for gallstone removal between patients withPAD and controls. Conclusions: PAD may not be considered a hinderance to ERCP success. Further research is needed to determine the best approach tocannulate the ampulla and provide endoscopic therapy for different subtypes of PAD.
Saslow, Sarah A.,Um, Wooyong,Pearce, Carolyn I.,Engelhard, Mark H.,Bowden, Mark E.,Lukens, Wayne,Leavy, Ian I.,Riley, Brian J.,Kim, Dong-Sang,Schweiger, Michael J.,Kruger, Albert A. American Chemical Society 2017 Environmental science & technology Vol.51 No.15
<P>Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)(2)(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (Fe3O4). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, Cr2O3, and Cr(OH)(3) phases. Spinel (modeled as Fe3O4), goethite (alpha-FeOOH), and feroxyhyte (delta-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)(2)(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (Fe3O4) and chromite (FeCr2O4).</P>
Enhanced <sup>99</sup>Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals
Um, Wooyong,Luksic, Steven A.,Wang, Guohui,Saslow, Sarah,Kim, Dong-Sang,Schweiger, Michael J.,Soderquist, Chuck Z.,Bowden, Mark E.,Lukens, Wayne W.,Kruger, Albert A. Elsevier 2017 JOURNAL OF NUCLEAR MATERIALS Vol.495 No.-
<P><B>Abstract</B></P> <P>Technetium (<SUP>99</SUP>Tc) immobilization by doping into iron oxide mineral phases may alleviate the problems with Tc volatility during vitrification of nuclear waste. Because reduced Tc, Tc(IV), substitutes for Fe(III) in the crystal structure by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation of Fe oxide minerals, two Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were prepared and tested for Tc retention in glass melt samples at temperatures between 600 and 1000 °C. After being cooled, the solid glass specimens prepared at different temperatures at 600, 800, and 1000 °C were analyzed for Tc oxidation state using Tc K-edge XANES. In most samples, Tc was partially (<60%) oxidized from Tc(IV) to Tc(VII) as the melt temperature increased up to 600 °C. However, most of Tc(IV) was completely (>95%) oxidized to Tc(VII) at temperature above 800 °C. Tc retention in glass melt samples prepared using Tc-incorporated Fe minerals were slightly higher (∼10%) than in glass prepared using KTcO<SUB>4</SUB> because of limited and delayed Tc volatilization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reduced Tc(IV) can be incorporated within an Fe oxide mineral structure. </LI> <LI> Tc-incorporated Fe minerals can increase Tc retention in glass waste forms. </LI> <LI> Increased Tc retention in glass can reduce the cost of waste treatment. </LI> </UL> </P>
Development of a Concept to Optimize the Energy Efficiency in Forging Process Chains
Denkena, Berend,Park, Hong-Seok,Behrens, Bernd-Arno,Henjes, Jan,Bertys, Sebastian,Dahal, Prakash,Luken, Ingo,Klassen, Andreas Korean Society for Precision Engineering 2013 International Journal of Precision Engineering and Vol.14 No.7
In the industrial production, approaches for the optimization of process chains mainly focus on criteria like quality, costs and time. Normally the energy consumption of process chains is not considered, although the variation of process parameters is an important possibility to reduce the consumption significantly. Besides that, the investigated processes are often optimized locally without considering the interaction between the different process elements of the whole process chain. Based on this background the developed concept realizes the optimization of the energy consumption of a forging process chain by adaptation of its energetic relevant parameters. Therefore, the concept defines at first variation intervals for the energetic most significant parameters of a forging process chain. After that, the resulting technical/technological modifications are evaluated energetically. To enable a holistic optimization of the process chain, the approach includes the use of a simulation model. The application of the concept has been approved with a simulation model of a 4-cylinder-crankshaft process chain. With the parameter variations 'reduction of the forging temperature', 'reduction of the raw part volume' and 'reduction of the forging time' three possibilities to reduce the energy consumption were identified successfully.